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KCFPKompetenscentrum Förbränningsprocesser

Centre of Competence Combustion Processes

Annual Report 2008

Faculty of Engineering, LTH Lund University

KCFPORGANISATION

BOARDSören Udd, Volvo Powertrain (Chair)Börje Grandin, Volvo CarsTommy Björkqvist, GM SwedenUrban Johansson, Scania CV

Ulla Holst, LTHMarcus Aldén, LTHPer Tunestål, LTHBernt Gustavsson, STEM

DIRECTORProfessor

Bengt JohanssonSupervisor for:

PPC, SACI

ADMINISTRATORMaj-Lis Roos

AssociateProfessor

Mattias RichterSupervisor for:

PPC

AssociateProfessor

Per TunestålSupervisor for:CC , SIGE and

SACI

AssistantProfessor

Öivind AnderssonSupervisor for:

GenDies

Associate Professor

Rolf EgnellSupervisor for:Fuel and PPC,

GenDies

ProfessorRolf JohanssonSupervisor for:

CC

ProfessorXue-Song BaiSupervisor for:

CM

ProfessorMarcus AldénSupervisor for:

PPC, SIGE,GenDies

AssociateProfessor

Martin TunérSupervisor for:

Fuel

ADMINISTRATORNina Mårtensson

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CONTENTS

1. Partially Premixed Combustion Project 4

High Load Partially Premixed Combustion with High Octane Number Fuels 4

Effect of strong pressure oscillations on wall temperature 6

2. Spark Assisted Compression Ignition Project 7

3. Combustion Control Project 9

A Physical Two-Zone NOx Model Intended For Embedded Implementation 9

Physics-based Modeling and Control of HCCI Engines 11

4. Combustion Modeling Project 13 Modeling of HCCI Combustion 13

5. SI Gas Engine Project 17

6. Fuel Project 19

Fuel Effects 19

7. Generic Diesel Project 21

Analysis of the Correlation Between Engine-Out Particulates and Local Φ in the

Lift-Off Region of a Heavy Duty Diesel Engine Using Raman Spectroscopy 21

Studies of Cold Start in a Light-Duty DI Diesel Engine 23

Formaldehyde and CO measurements 24

8. Publications and Patents 26

KCFPCentre of Competence Combustion Processes

PROJECTS

Partially Premixed Combustion Project (PPC)

Spark Assisted Compression Ignition Project (SACI)

Combustion Control Project (CC)

Combustion Modelling Project (CM)

SI Gas Engine Project (SIGE)

Fuel project (Fuel)

Generic Diesel project (GenDies)

The centre of competence combustion processes, KCFP, started July 1 1995.

The main goal of this centre is to better understand the combustion process in internal combustion engines. Of particular interest are the combustion processes with low enough temperature to suppress formation of NOx and particulates, PM, often called Low Temperature Combustion, LTC or homogeneous Charge Compression Ignition, HCCI.

The centre of competence combustion processes has a budget of 23.9 MSEK per year. This is roughly one third each from the Swedish Energy Agency, STEM, Lund University and Industry.

The industry partners are Volvo Cars, Volvo Powertrain, Volvo Penta, Saab/GM, Scania, Toyota, Nissan, Caterpillar, Cargine, Chevron, Finnveden, Hoerbiger (former Mecel), Loge, Wärtsilä Diesel, and the Swedish Gas Centre, SGC.

Layout: Nina MårtenssonPrint: Media-Tryck, LU, 2009

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High Load Partially Premixed Combustion with High Octane Number FuelsVittorio Manente

By injecting high octane number fuels in a compression ignition engine longer ignition delay can be achieved as compared to Diesel. Because of the long ignition delay, when combustion starts, the air-fuel mixture is fairly homogeneously distributed. Homogeneous combustion results in less soot, in addition if EGR is added the combustion temperature is low thus Nox can be kept within the desired range. If a separation is achieved between the end of the injection and the start of the combustion, the burning rate is kinetically controlled. If kinetically controlled combustion is correctly phased and the combustion duration is between 10 and 30 CAD, high efficiency can be obtained.

The objective of studying high octane number fuels in partially premixed combustion, PPC, was to understand if there is a way to achieve: low NOx, low soot, high efficiency and acceptable pressure rise rate from medium to high engine load.

A single cylinder Scania D12 was used for the investigation. The engine was ran at 1000 rpm, Gasoline and Ethanol were the fuels under examination.

To properly run high octane number fuels in PPC mode and achieve the previously mentionedV targets, an advanced injection strategy was developed. The injection strategy consisted of two injections. The first one, very early in the cycle, is used to create a homogeneous mixture while with the stratification created by the second the combustion is triggered. The phasing and the load are controlled with the second injection. As the load increases, EGR is added to avoid early ignition of the first injection.

This advanced injection strategy was developed because it was found that a large separation between the end of injection and start of combustion results in high pressure oscillations that are capable of breaking the thermal boundary layer thus heat transfer is enhanced leading to poor engine efficiency. A boost pressure sweep was performed with Gasoline and Diesel at constant fuel rate. Much higher pressure oacillations were achieved with Gasoline; as consequence the heat transfer increased (see Figure 1).

1. Partially Premixed Combustion ProjectPartially Premixed Combustion, PPC, is a combustion process between Homogeneous Charge Compression Ignition, HCCI and the classical diffusion controlled diesel combustion. With PPC it is possible to moderate the charge inhomogeneity and thus control the burn rate better than with HCCI. In comparison to classical diesel combustion the NOx and particulates can be suppressed with orders of magnitude.

Within the PPC project there have been substantial activities 2008 on PPC type of combustion with a range of fuels and engine types. The Ph.D. student, Vittorio Manente has been running a Scania truck size diesel engine with PPC type of combustion using diesel fuel as well as high octane fuels like gasoline and ethanol. Mixtures of diesel and ethanol and gasoline /ethanol were also tested. In contrast to the results presented in the annual report 2007 the engine has been operated with increased inlet pressure and hence load. Tests have also been conducted in a car size diesel engine, the Volvo D5, in collaboration with the fuels project. Late in the year laser experiments were carried out in the Scania D12 engine with laser induced phosphorescence, LIP, on combustion chamber walls to investigate the wall heat transfer increase due to sever pressure oscillations that can occur with too homogeneous mixtures.

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Figure 1: Heat transfer as a function of boost pressure (left) and pressure rise rate as a function of the cycle number (right).

Results

The advanced injection strategy was tested with Gasoline and compared to classical Diesel combustion. Low NOx and low gross indicated specific fuel consumptions were achieved up to 16 bar IMEP. Soot was around 5 FSN as a result of the obsolete injection system (1000 bar as common rail pressure and 0.18 mm as nozzle orifice diameter). The results are shown in Figure 2. Because the start of the combustion was not fully separated with the end of the injection, the pressure rise rate was kept below 15 bar/CAD. In terms of gross indicated fuel consumption, Gasoline and Diesel had 174 and 186 g/kWh respectivelly.

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Figure 2: Heat release rate, injection signal and cylinder pressure for Gasoline with this advanced combustion mode (left), emissions for Diesel and Gasoline (left).

Ethanol was also tested with this advanced injection strategy at 16.76 bar gross IMEP. NOx and soot were 0.17 and 0.008 g/kWh respectively; the emissions were below EURO VI limits without using any aftertreatment system. The gross indicated efficiency was 47% while the pressure rise rate 10 bar/CAD. Figure 3 shows the combustion behavior of Ethanol. Because of the longer ignition delay, high ON fuels mixe better with air prior combustion thus resulting in combustion efficiency higher than 97% even with 45% of EGR see Figure 4.a

Vittorio ManentePhD Student

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Figure 3: Heat release rate, injection signal Figure 4: Combustion efficiency as a function and cylinder pressure for Ethanol. of the start of the pilot injection and pilot- main ratio at high load with Ethanol.

Effect of strong pressure oscillations on wall temperature Johannes Lindén, Christoph Knappe, Vittorio Manente

In the PPC project it has been noted that severe pressure oscillations at high load have a strong negative effect on the efficiency. In this PPC sub-project the in-cylinder wall temperature will be measured in order to investigate the high pressure oscillations ability to break the thermal boundary layer and thus enhancing heat transfer.

The chosen technique is based on what is referred to as thermographic phosphors. This is an optical technique that is non intrusive and capable of remote probing.

In short: The surface of interest is coated with a thin layer of a suitable thermo sensitive material (thermographic phosphor). Then the coating is illuminated with laser radiation and shortly thereafter, when the excited material relaxes, light is emitted. This resulting radiation from most thermographic phosphors has a lifetime which is dependent upon the temperature. The intensity decays exponentially in accordance with

where I0 is the initial emission intensity, t is time and τ is the lifetime time constant of the phosphorescence involved i.e. the time taken for the intensity to decrease to 1/e of the initial emission I0. The phosphorescence lifetime of the phosphor material decrease with increasing temperature. The temperature can thus be calibrated to the lifetime and be reproduced by calculating the phosphorescence lifetime from the measured decay in intensity. This is normally done by fitting the intensity decay to the theoretical model, using a non-linear fitting procedure. The error in temperature in such a measurement vis ideally less than 1%. A similar technique was successfully

applied within the KCFP a few years ago with the thermographic phosphor La2O2S:Eu. Since then the involved researchers have continued the development of this technique and among others this has resulted in new thermographic phosphors. In the ongoing measurement campaign CdWO4 is being used. This phosphor emits blue light which makes it less sensitive to interferences from soot radiation. The lifetime is shorter which enables even higher time resolution <2µs. Furthermore the signal strength is also enhanced compared to the previous used material. At present preliminary measurements have been performed in the one-cylinder Scania engine and calibration measurements is ongoing.

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Figure 1. Schematic view of the experimental setup. UV laser radiation excites the phosphor and the red-shifted phosphorescence is detected with a photo-multiplier.

Johannes LindénPhD Student

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2. Spark Assisted Compression Ignition (SACI)Patrick Borgqvist , Bo Li

Spark Ignition (SI) engines struggle with low efficiency at part load operation. A feasible way to improve low load efficiency for cars currently running with SI engines would be to use an engine that can run in homogenous charge compression ignition (HCCI) mode at part load and switch to SI at high load. Studies have reported high efficiency and low NOx emissions compared to the SI-engine. To achieve mode switching from SI to HCCI and vice versa the intermediate region where both combustion modes coexist i.e. SACI combustion is of interest and is the main target for this project. Also the usage of spark assistance is of interest to control combustion timing and to increase the possible operating range in HCCI mode.

Preliminary resultsThe research engine, seen in Figure 1, is a passenger car size Volvo D5 which has been converted to single cylinder operation. The CI cylinder head has been replaced by a pent-roof 4 valve SI cylinder head with optical access. Optical access is achieved through an, approximately, 20 mm diameter sapphire window, as seen in Figure 2. The spark plug can be seen in the center of the window.

Figure 1. The Volvo D5 research engine with optical access.

The lift profiles of the pneumatic valve train differ from that of a traditional cam shaft, as seen in Figure 3. The valve lift is measured with a MicroStrain displacement transducer mounted directly under the valve actuators. The valve lift profile for each cycle is recorded simultaneously with the pressure trace.

The engine is equipped with a combined spark plug and pressure sensor, port fuel injector and a fully flexible pneumatic valve train system supplied by Cargine Engineering.

The valve train system consists of four actuators, one for each valve, fitted directly on top of the valve stem. The valve train system is working with pressurized air to achieve valve lift.

Figure 2. Optical access window through the cylinder head.

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Figure 3. Measured valve lift profiles of exhaust and intake valves with negative valve overlap

HCCI is achieved through trapping of hot residuals from the previous cycle. This imposes a limit on achievable low load since, eventually, the temperature of trapped residuals will get too low and the amount too high to sustain proper combustion.

In an ongoing measurement campaign, the residual gas concentration is measured crank angle resolved using IR measurement technology. Carbon Dioxide features strong emission and absorption around 4.5 µm. In these experiments the emission is utilized for cycle resolved, in-cylinder, measurements. The probing can typically be performed at several kHz giving true crank angle resolved data, something that is not possible with conventional exhaust analysis. Figure 4 shows an example from a similar application in a two-stroke engine.

Figure 4. Example of cycle-resolved probing of carbon dioxide in a two-stroke engine. CO2 (Blue) and pressure (red).

Using cycle resolved pressure trace and valve lift profile data, the purpose of this measurement campaign is to deepen the understanding of the interaction of valve timings on residual gas concentration and the subsequent combustion. In future experiments, this information could also be used for control oriented modeling purposes where combustion phasing control is an interesting challenge for HCCI combustion.

Patrick BorgqvistPhD Student

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3. Combustion control ProjectThe Control Project within KCFP focuses on control and control oriented modeling of combustion. Two PhD students, Anders Widd (Dept. of Automatic Control) and Carl Wilhelmsson (Dept. of Energy Sciences), are active in the project under supervision of senior researchers Per Tunestål (Energy Sciences) and Rolf Johansson (Control).

During the year a computationally efficient Nox model for Diesel combustion has been developed and partially validated. Model predictive control of HCCI combustion based on a physical model of combustion and heat transfer has also been developed and experimentally validated.

A Physical Two-Zone NOx Model Intended For Embedded Implementation

Carl Wilhelmsson

In the automotive industry models are commonly used mainly for three purposes; calibration, analysis and control. A NOx model has been developed which is intended for engine control.

Computational ease is hence much more important than maximal accuracy and full physical interpretation. Physical models of different kinds can be used for engine control. Physical models are often preferred over ‘black-box’ (empirical) models due to their more general nature. If a model successfully captures physical phenomena common for, in this case, engines, the model calibration effort hopefully decreases when adopting the model in different contexts (on different engines). Physical models can often be used both for prediction and indirect measurement.

The model, or algorithm, developed implements a physically correct NO model which uses a two zone approach to model the stratified nature of Diesel combustion. There is one burned zone in which the NOx formation takes place and one unburned zone composed of only air, as explained by Fig. 1. Using this method and algorithm the physical interpretation can be maintained while the algorithm is significantly simplified.

Figure 1. A two-zone modeling concept.

If the pressure in the cylinder is known (which is a basic condition for much combustion engine related modeling) it is possible to compute the global temperature as well as the temperature of the unburned zone using a number of assumptions. Furthermore it is possible to compute the number of moles in the burned zone using ’conventional’ heat release analysis. It is also possible to compute the total number of moles in the combustion chamber and hence the number of moles in the unburned zone. When the number of moles in the unburned zone, burned zone and globally is known as well as the temperature globally and in the unburned zone it is possible to compute the temperature of the burned zone. A more extensive model of the combustion is hence not needed to compute the temperature of the burned zone. It is possible to avoid a direct computation of burned zone temperature and the related complex and iterative numerical solution of an energy balance ’normally’ used to determine burned zone temperature and mole content.

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Figure 2. Mean temperature of the different zones using the described algorithm.

Figure 3. Modeled NO content of the cylinder as a function of crank angle.

Since NOx emissions mainly consist of NO, NO is modeled rather than NOx. NO formation results from high temperatures in the burned gases created by combustion, hence the temperature of the combustion products (the burned zone) is a key variable for computing NO emissions. The methods for computing NO knowing the burned zone temperature are fairly well known and straight forward. To compute the NO formation rate a novel variant of the well known ’Zeldovich’ mechanism (here called the ’modified Zeldovic mechanism) was developed and used. The original Zeldovich mechanism had to be corrected for varying burned zone volume.

The only ’tuning-parameter’ within the model is the local lambda at which combustion takes place. The model provides best agreement with measured data when the local lambda is within physically reasonable values (lambda is close to one). The local lambda is also well below the global, measured, lambda indicating that the model mirrors the stratified conditions during Diesel combustion.

The performance of the model has been screened showing that the model gives sufficiently accurate results considering the coarse nature of the model. On five data points an absolute average error of 20% was obtained, the maximum error using a fixed local lambda of 1.088 was about 30%. Even though this number is not to be considered as a very good result compared to extensive multi-zone models it is, using the model, possible to get quantitative information regarding the instantaneous NO content in the cylinder. This work should be understood in the context of control oriented, on-board (embedded) implementable models. Comparing with complex multi-zone models is unfair considering the computation times needed to complete the different models. Using the suggested algorithm with pre-computed parts it is most likely possible to obtain information regarding the NO content during the cycle! Information that might prove useful when implementing for example feedback Diesel combustion control.

Carl WilhelmssonPhD Student

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Physics-based Modeling and Control of HCCI EnginesAnders Widd

In this project model-based control of HCCI is investigated. A cycle-resolved model of HCCI including cylinder wall temperature dynamics has been developed previously in the project. The model consists of nonlinear equations relating the temperature state of the present cycle and the control signals to the temperature state of the next cycle. The equations assume isentropic compression and expansion and auto-ignition is predicted using a simplified Arrhenius-integral independent of species concentration.

During the year the model was reformulated to have the indicated mean effective pressure, IMEP, and the crank angle of 50% burned, θ50, as states. This removed the need for estimating the system’s state from output measurements. For the control design, the model was linearized around an operating point, yielding a linear system with 2 inputs and 2 outputs. The inputs used for control were the crank angle of inlet valve closing, θIVC, and the intake temperature, Tin.

The linearized model was used to design Model Predictive Controllers. The basic idea of Model Predictive Control (MPC) is to find a sequence of future control signals that minimize a cost function penalizing the predicted future output errors and control usage. The minimization is performed while respecting explicit constraints on both inputs and outputs. Once the optimal control sequence has been found, the first step of this sequence is implemented. At the next sample, the optimization is repeated with the current state as initial condition.

Initially, a controller for simultaneous control of IMEP and θ50 was designed. Simulations indicated that it was advantageous to use several linearizations and switching depending on the operating point. This allows linear control design techniques to be used but captures more of the nonlinear behavior than using a single linear model. The intake temperature was governed by an electric heater with a slow response, which had a negative effect on the resulting control performance. To improve on this, a first-order model of the heater dynamics was incorporated into the model so that the measured intake temperature could be used to generate the control signals. The controller was experimentally tested and performed similarly to the simulations.

As a second approach, only control of θ50 was considered. The control signals can only affect IMEP slightly and the load control could therefore be handled by varying the amount of fuel directly. Instead of using only the heater a system for Fast Thermal Management (FTM) was implemented. The intake air was a mixture of a cooled air flow and the flow past the heater. The control signals were the heater power and the two valve positions. A mid-ranging controller was designed to keep the intake temperature at the desired value and the valves in the middle of their operating range. This yielded a considerably faster response to changes in the desired intake temperature.

Figure 1: Principle for fast thermal management and step response for intake temperature.

The θ50-controller was then evaluated experimentally in terms of performance and robustness towards disturbances. The controller follows set-point changes relatively fast over a large range of values. Changes of a few degrees around the linearization point are accomplished in approximately 10 engine cycles and longer steps, such as from +4 to -3 CAD take approximately 15 engine cycles.

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Figure 2: Response to steps of increasing amplitude.

The robustness towards disturbances in the engine speed, the injected fuel energy, and the amount of recycled exhaust gases (EGR) was investigated experimentally. The system maintained the desired combustion phasing during all three disturbances. The EGR had the most prominent effect on control performance. One reason for this is that the EGR level alters the thermal properties of the charge. Also, the change in EGR is not reflected in IMEP, which is used as a measurement in the controller.

Figure 3: Response to disturbances in engine speed, fuel energy, and EGR level.

For the multi-cylinder case, identical controllers were used for all cylinder. As the intake temperature is a global variable shared by all cylinders, only one cylinder was allowed to change it. The required inlet valve closing for the different cylinders showed a large spread. There is a risk of saturating the inlet valves of the cylinders far away from the cylinder governing the intake temperature. This could be handled by instead implementing the average of the requested intake temperatures.

Anders WiddPhD Student

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4. Combustion Modeling ProjectExperiments and laser diagnostic studies within KC-FP have shown that HCCI combustion is sensitive to the in-cylinder flow, piston geometry and operating conditions. A highly stratification temperature field, generated by for example piston bowl geometry and/or exhaust gas recirculation, could affect the ignition timing of the charge, the combustion duration, and thereby the pressure rise-rate. This information is useful for developing control strategies in the future HCCI engine design. However, there is a lack of understanding of the fundamentals of turbulence/heat transfer/chemistry interaction in the HCCI combustion process. To gain improved understanding of the HCCI combustion process, combined engine experiments, laser diagnostics and modelling activities are organized within KC-FP. The aim of the modelling project is to apply high fidelity spatially and temporally resolved numerical models (large eddy simulation) to simulate the detailed three dimensional flow and ignition kernel structures in the cylinder. The numerical simulations are used to assist the experiments to identify the onset of temperature stratification in the cylinder, the development of turbulence in different strokes of the cycle, and the mechanisms of ignition kernel/thermal stratification/turbulence interaction. The focus in the past year has been on the ethanol air combustion in different engines and under different conditions, including the metal and optical experimental Scania engine and Volvo engine, under HCCI and SACI conditions, with and without negative valve overlap. The results indicate that the onset of auto-ignition is more sensitive to the stratification of temperature field than to the fuel/residual gas stratification; the bowl geometry and cooling conditions can affect the temperature stratification to such an extent that the pressure-rise-rate can be significantly altered. The length scales of the temperature stratification are shown to also play a role on the ignition front propagation and combustion duration.

Modeling of HCCI CombustionIn 2008 HCCI combustion processes in two different engines have been considered in the modeling project with both homogeneous and stratified charges. One is a six cylinder Scania D12 truck sized engine that was modified to HCCI engine with port fuel injection, and the other is the Volvo D5 engine with negative valve overlapping (NVO) and port fuel injection. Additionally, we have looked into the onset of temperature stratification in a Toyota engine. Corresponding experiments have been carried out in the PPC sub-project [1,2], the SACI sub-project [3,4], and a related project sponsored by Toyota. Large eddy simulation (LES) models are used to simulate the development of temperature field, the fuel/residual gas mixing and the auto-ignition process. The results are exemplified as follows.

Auto-ignition of lean ethanol/air mixture in Scania D12 engine

Rixin Yu, Tobias Joelsson

Large eddy simulation of ethanol/air combustion in HCCI engines (modified based on the Scania D12 engine) are carried out to understand the experimentally observed combustion characteristics in two experimental engines. The two engines have nearly the same geometry, compression ratio, and operating conditions. The cooling of the walls for both engines is similar; it is cooled by circulated water. The cooling of the pistons in the two engine is however different. For the metal piston it is cooled by an oil spray from beneath whereas the quartz piston is cooled by air. Experiments show that the quartz engine has a slower pressure-rise rate and lower combustion efficiency than that of the metal engine, when the two engines are made to have the same ignition timing by adjusting the intake gas temperature.

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Figure 2. (left figure) In-cylinder pressure and normalized accumulative heat release (c) in the metal piston engine from LES and experiments, (right figure) In-cylinder pressure and c in the quartz piston engine from LES and experiments, Tin1 = 354K Tin2 = 388K.

LES results revealed the development of turbulence and temperature stratification in the two engines (Figure 1). It is shown that the two engines have minor difference in the turbulence field. They both show a peak turbulence at about 50 CAD after the intake valve opens; they also show a peak of turbulence at the TDC where the fluid in the bowl exchanges with fluid in the squish region.The temperature stratification in the optical engine is much higher than that in the metal engine since the quartz piston is hotter. It is shown that both mean temperature and temperature stratification at the end of the intake stroke increase almost linearly as the wall temperature increases with a constant intake gas temperature. The experimentally observed slower pressure-rise-rate in the quartz engine is successfully simulated (Figure 2). From the LES results it is seen that the main reason for this slower combustion in the quartz engine is the existence of the larger temperature stratification due to the hotter piston, and the lower intake gas temperature set in the experiments. The LES predicted that if the intake temperature is set to be the same as that in the metal engine, the combustion efficiency would increase by 20%, but the pressure-rise rate and peak in-cylinder pressure and combustion phasing would also increase considerably.

Details of the results are published in Joelsson et al. (SAE 2008-01-1668).

Figure 1. Instantaneous temperature field (on the 2D cut planes) with 3D streamlines (red/dark lines) and 3D iso-surface of lambda-2 eigen-values of strain rate tensor (white/grey) in the metal engine (obtained from LES).

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Effect of temperature stratification on HCCI combustion

Numerical simulations of ethanol/air combustion with a relative air/fuel ratio of 3.3 in the Scania D12 HCCI engine are carried out using different modeling approaches, i.e. the multi-zone simulation which neglects the flow effect on chemical reactions and the large-eddy simulation approach with a reaction progress variable tabulation model. Detailed chemical reaction mechanisms of Marinov [5] are used in the simulations. Systematic investigation of the hot/cold spots with different length and amplitude of temperature stratification is carried out. It is found that the effect of temperature stratification on HCCI combustion has a general trend that with higher temperature stratification the mixture will become easier to auto-ignite and thus with a similar mean temperature and flow condition, the auto-ignition will happen earlier. With the same combustion phasing (i.e. the same CA10), the higher the temperature stratification is, the longer the combustion duration will be. This trend can be predicted qualitatively well by the multi-zone model neglecting the effect of turbulence and flow.

Figure 3. Temperature field in a cross-axis section at different crank angles showing the ignition of hot spot with difference sizes and T’=35K. First row: initial hot/cold spot size: Ix = L/20, I = L/2 ; Second row: initial hot/cold spot size: Ix = L/20, I = L/8; Third row: initial hot/cold spot size: Ix = L/20, I = L/16.

The length scale of the stratified temperature field plays an important role in the auto-ignition process. With the same initial mean temperature and stratification, smaller hot spots tend to auto-ignite later since smaller hot spots are smeared more by turbulent eddy transport (Figure 3). It is interesting to note that for hot spots that are larger than the integral scale (large) eddies the auto-ignition timing is rather insensitive to the hot spots size. In general, the combustion duration for smaller hot spots is shorter than that of larger hot spots due to the smeared temperature field of the small hot spots that leads to lower temperature stratification. However, for very small hot spots the auto-ignition occurs too late (after the piston passes TDC). In such case, expansion of the combustion chamber lowers the in-cylinder pressure and temperature, which leads to slower combustion and even incomplete combustion.

With the same auto-ignition timing larger hot spots have longer combustion duration since the transport of hot gas in the combustion zone to the cold zone is less effective when the hot spot size is large. This trend is rather monotonic when the temperature stratification is high. With low temperature stratification (rms value) a particular hot sport size (on the order of the length of integral scale eddies) tends to have faster combustion. This is a result of turbulence/ignition front interaction.

Details of the results are given in Yu el al. (SAE 2008-01-1669).

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Effect of NVO on HCCI combustionThe effect of negative valve overlap on the mixing, heat transfer and ignition process in a personal car size HCCI engine (modified based on the Volvo D5 engine) is studied using large eddy simulation and multi-zone modeling based on detailed chemical kinetics.

As expected, different NVO generates different mixing and temperature fields. With large NVO the mixing time is shorter and the amount of in-cylinder residual gas is higher. There are several mechanisms that control the mixing and heat transfer process. The wall heat transfer initially has an effect of cooling the residual gas, causing an elevated temperature stratification but not concentration stratification. The inhale of the fresh intake gas contributes both to the formation of temperature stratification and concentration stratification. Turbulence in the later stage of the mixing process tends to smear out the temperature and concentration stratification.

Figure 4. Ignition behavior of different zones for the case of NVO 80. The solid bold line denotes the zone that ignites first and dashed bold line the zone ignites last. The left figure shows that the first ignited zone has the highest temperature and last ignited zone has lowest temperature; the right figure shows that the first ignited zone is leaner than the last ignited zone.

The temperature field and the concentration field are closely correlated each other. Since the residual gas has higher temperature than the intake gas, the high temperature zones are most frequently (on mass basis) the zones with high amount residual gas.

The ignition events are more closely correlated to the temperature field than to the concentration field. Zones that ignite first are the ones with highest temperature but leaner fuel and higher residual gas (Figure 4.).

Future WorkIn 2009 we will place our attention more on the PPC process, namely to consider fuel stratification and their ignition behavior. We will make use of direct numerical simulation approach with fine grid resolution to investigate the ignition core development in the context of PPC. We will also consider NVO and SACI combustion process and plan to develop models for SACI within the framework of LES.

Tobias JoelssonPhD Student

Rixin YuPhD Student

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5. SI Gas Engine Project Mehrzad Kaiadi

Heavy duty Spark Ignition (SI) Natural Gas (NG) engines have lower efficiency than the heavy duty Diesel engines. This lower efficiency is due to partly the lower compression ratio used in NG engines and also the throttling losses especially at low/part loads. The maximum load is also limited in SI NG engines due to higher exhaust gas temperature and also lower compression ratio. The main objective of this project is to achieve Diesel engine efficiency, Diesel engine maximum load range and SI engines efficiency. High EGR rates combined with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy duty SI NG engines. With stoichiometric conditions a three way catalyst can be used which means that regulated emissions can be kept at very low levels. To enable good combination of load, efficiency and emissions the engine must run with closed loop combustion control.The gas engine project has involved one senior researcher, Associate Professor Per Tunestål, and one PhD student, Mehrzad Kaiadi. Both are with the combustion engine division and have been active in the project for the full duration of 2008.

Experimental setup and Control system

The research engine, seen in figure 1, is a 9.4 liter from Volvo. The engine is equipped with short route cooled EGR system and also turbocharger with Wastegate. Single-point injection system of the engine is replaced by a multi-port injection system. The main reasons for this change are that, the engine responds faster to throttle changes which make it possible to implement more sophisticated regulators. It also makes it possible to inject fuel individually for each cylinder which helps in balancing the cylinders.

Figure 1. The 9.4 liter Volvo engine.

A master PC based on GNU/Linux operating system is used as a control system. It communicates with three cylinder-control-modules (CCM) for cylinder-individual control of ignition and fuel injection via CAN communication. Crank and cam information are used to synchronize the CCMs with the crank rotation. Flexible controller implementation is achieved using Simulink and C-code is generated using the automatic code generation tool of Real Time Workshop. The C-code is then compiled to an executable program which communicates with the main control program. The controllers used for this experiment are lambda, load and EGR controller which determine the offset amount of fuel, air and EGR. The controllers can be activated from the Graphical User Interface (GUI).

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Studies performed

Increasing Efficiency at Low/Part loads The main focus of this study is to reduce the throttling losses by means of EGR. The addition of inert exhaust gas into the intake system means that for a given power output, the throttle plate must be opened further, resulting in increased inlet manifold pressure and reduced throttling losses. By increasing EGR the specific heat ratio will be slightly lower and combustion duration will be longer but it can be compensated somewhat by advancing the ignition timing.

There is a limit to the amount of EGR that can be tolerated for each operating point. A combustion stability parameter should indicate the EGR tolerance of the engine. Different combustion stability parameters derived from pressure and ion-current signals are applied in order to control the dilution limit with EGR. Furthermore closed-loop lambda control is applied to control air/fuel ratio. With help of these controllers and also a load controller, a tool is developed for finding the best positions of the throttle and EGR valve where the engine has its highest dilution while the engine stability is preserved.

Two papers are written based on the results of this study i.e. in the first one the combustion stability is based on the pressure signals and in the second one the combustion stability is derived from ion-current signals. The proposed control strategy has been successfully tested on a heavy duty 6-cylinder port-injected natural-gas engine and the results show 1.5-2.5 % units improvement in Brake Efficiency.

Using Hythane as a fuel in the engine In another experiment, behaviour of the engine was investigated by running the engine with Hythane (Natural gas + 10% Hydrogen by volume) when the engine operates stoichiometric. Data from running a lean burn natural-gas engine with Hythane was available and it was desired to see the behavior of the engine with stoichiometric operation. The results do not show significant changes in knock margins, efficiency and emissions with stoichiometric operation. However, Lean limit and dilution limit can be extended somewhat by Hythane.

Planned ActivitiesImplementing more advanced control strategies will be used to maximize the reliability for obtaining the same efficiency and emissions levels with the transient conditions as with steady state. Model Predictive Control (MPC) will be used to control lambda which will be modeled using System Identification.

Do some modifications on the engine which enable us to extend the dilution and maximum load limits. These changes are:

o Replacing the pistons of the engine with a high turbulent pistons

o Increasing the compression ratio from 10.5 to 12

o Changing the EGR system to increase the EGR capacity

o Changing the ignition system to deliver more energy

Transient running of the engine at higher loads will take place.

Mehrzad KaiadiPhD Student

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6. Fuel ProjectIn not a too distant future we will phase a situation where automotive fuel of today’s standard will not be available any longer, at least at a reasonable price. The first reason is that we could not allow ourselves to use fuels that increase the greenhouse effect, i.e. using fossil derived fuels. The second reason is that the oil reserves are gradually being exhausted. The only feedstock available for future fuel production is biomass. Fossil feedstock in combination of carbon sequestration is another possibility, but this approach is too uncertain to serve as the only option.

Today’s consumption of oil is about 4000 million tonnes per year. Very few believe that it is possible to replace the corresponding amount of energy with bio energy. Thus it is mandatory to use the available biomass in the most effective way. Hence, any fuel/engine combination must be rated after its well-to-wheel efficiency. The diesel engine is presently the most efficient combustion engine. Consequently, the challenge is to combine the diesel engine with bio fuels with high well-to-tank efficiency. Advanced processes and refinement, in order to standardize the fuel properties despite the feedstock, cost energy. A possibly more fruitful approach is to allow a certain degree of variations in fuel properties and compensate for them by engine adaptation.

Fuel EffectsUwe Horn

During the first part of the Fuels Effects project, special attention has been paid on FAME type fuels. The special characteristics of this family of fuels have been identified and related to observations concerning energy release and emissions formation. In addition, different approaches to compensate for unfavourable differences compared to standard diesel fuels. The project has involved the PhD student Uwe Horn and the supervisor Associated Professor Rolf Egnell. Most of the research during 2008 has been focused on how the physical properties of the fuel affect the spray formation and how the spray characteristics in its turn affect energy release and emission formation. The work has consisted of literature studies concerning models for spray behaviour and geometries, spray studies in an optically accessible engine and experiments in a metal engine. The fuels studied during 2008 where PRF0 (n-heptane), MK1 (Swedish Environmental Class I diesel fuel), B100 (SME) and GTL (a synthetic diesel fraction with a distillation range close to the one of SME).

Spray models The literature study concerning spray models revealed that the fuel and ambient densities has a major impact on spray angle. The spray penetration length is dependent on injection pressure, ambient density, injector geometry, and injection duration. Fuel properties that influences the liquid lengths are: 50% distillate temperature and latent heat of vaporization.

Optical engine results

Figure 2: Transparent Engine Setup Figure 1: Transparent Engine Setup

mirror

transparent piston

cylinder head Volvo NED5

transparent cylinder liner

combustion chamber

extended piston

cylinder extension

dispersive light source

dispersive light source

liquid phase fuel spray

hi-speedcamera

mirror

transparent piston

cylinder head Volvo NED5

transparent cylinder liner

combustion chamber

extended piston

cylinder extension

dispersive light source

dispersive light source

liquid phase fuel spray

hi-speedcamerahi-speedcamera

The experiments in the optical engine were carried through by illuminating the spray as shown in Figure 1 to the right. In order to avoid self-ignition during injection, the engine was fed with inert gas from a domestic burner. The spray appearance was captured with a high speed video camera. A typical image of the spray is shown in Figure 2.

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The main spray geometry parameters like spray angle, penetrations length and penetration speed was calculated from the pictures by means of image processing and correlated to fuel data and to the established spray theories. Information from the inner circle in figure 2 was used to calculate spray angle and. The spray penetration length calculation was based on information between the red and the yellow circles.

Metal engine results The data from the optical engine experiment were used to make simple regression models that were used to transfer the information to metal engine conditions. In Figure 4 below is shown the “measured” spray length at start of combustion vs. injection pressure in the metal engine. Also shown are ignition delay (ID) and combustion efficiency (hc).

Figure 3: ID, Measured Liquid Spray Length at SOC Figure 4: HR characteristics vs. injection pressure and combustion efficiency vs. injection pressure

The impact of the fuel and the injection pressure own the heat release is shown in figure 4. As can be seen there are distinct differences in spray length at start of combu for the different fuels and injections pressures. For example, the high volatility of PRFO gives an opposite relation between injections pressure and liquid spray penetration than the other fuels. The high volatility also has in impact premixed heat release rate.

Conclusion regarding the impact of injection pressureThe injection pressure is an important control parameter in order to compensate for fuel dependent differences in atomisation due to fuel volatility. For modern Diesel engines with high injection pressures, an improvement in mixture properties due to atomisation declines when droplet limited vaporisation is not longer the restricting mechanism. For low load conditions however, less volatile fuels (i.e. B100, GTL-distillate) might require a compensation of inferior atomisation properties by increased injection pressure.

Future work The PhD student Uwe Horn decided to finish his studies with the degree of licentiate in engineering. In addition the supervisor Rolf Egnell is approaching his retirement. Thus, the future supervision within the Fuel effects project will be carried through by Rolf Egnell’s successor Martin Tunér.

The recruitment for a successor to Uwe Horn is ongoing. The task of the new PhD student will be to look deeper into the chemical aspects in terms of auto-ignition and combustion rate for fuels used under engine conditions and time-scales. By combining experiments with kinetics simulations and the employment of multivariate tools, also on the existing data, correlations on a more profound level can be studied. These studies are expected to lead to publications at SAE, PCCP (Physical Chemistry, Chemical Physics) and Combustion and Flame.

Uwe HornPhD Student

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7. Generic Diesel ProjectThe diesel engine is an important power source for road transport. This is mainly due to its relatively low fuel consumption. As demands on fuel efficiency increase, the diesel engine can be expected to increase its importance in the future. Its main drawback has traditionally been the levels of exhaust gas emissions, particularly of oxides of nitrogen and particulate matter, mainly soot.

One focus of the GenDies activities during the last year has been the causes for soot trends from heavy duty diesel engines. In these engines a large part of the combustion process takes place during fuel injection in a more or less stationary flame. Soot is formed in fuel-rich zones inside the fuel jets. It is later oxidized in the diffusion flame at the periphery of the jets where it is mixed with the surrounding air. The amount of soot in the exhaust gases is determined by these two competing processes—soot formation and soot oxidation. Many of the research efforts in our field have focused on the formation process and how it is governed by air-entrainment into the spray upstream from the diffusion flame. By careful experiments the GenDies project has now shown that these processes close to the nozzle do not explain the variations in the soot emissions measured during the experiment. The experiments were performed in an optical heavy-duty diesel engine. The results rather indicate that the oxidation process is the dominating mechanism behind the soot trends. Future research will concentrate on clarifying the mechanisms further.

Another focus has been the combustion process during engine starting at extremely low temperatures, approaching -30 °C. Optical investigations of combustion during engine starting provided new insights into the origin of cold starting problems. Based on these insights, new injection strategies were developed that significantly improved engine startability and stability in cold climate.

Analysis of the Correlation Between Engine-Out Particulates and Local Φ in the Lift-Off Region of a Heavy Duty Diesel Engine Using Raman SpectroscopyUlf Aronsson

Heavy duty diesel engines tend to be operated at high loads where the long injection durations produce a combustion process that is largely spray-driven. A useful picture for understanding emission formation in these engines is that of a lifted flame on a stationary jet. This is because the diesel spray can be considered to behave as a quasi-stationary jet during the major part of combustion. Engine-out PM emissions can be seen as the result of two competing processes: soot forming and soot oxidation. The amount of soot produced depends on the soot forming rate and the residence time. The soot forming rate mainly depends on two variables: the combustion temperature and the equivalence ratio, Φ Soot is mainly formed at temperatures above 1700 K in zones where Φ>2 [1]. Entrainment of hot air upstream of the lifted diffusion flame is therefore important for the soot forming in the jet.

The local equivalence ratio, Φ, was measured in fuel jets using laser-induced spontaneous Raman scattering in an optical heavy duty diesel engine. An average image from the Raman measurements can be seen in Figure 1. The center of the jet represents 0 mm on the vertical axis. The graph to the right in Figure 1 shows the corresponding Φ values along the laser beam. Φ was calculated from the relative Raman signal strength between O2 and CH (fuel), see Figure 1.

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Figure 1. A Raman spectrum taken in the engine. The y-axis denotes distance along the laser beam in mm and the abscissa indicates the Raman shift in cm-1. The graph to the right shows the corresponding Φ values along the laser beam.

The objective was to study factors influencing soot formation, such as gas entrainment and lift-off position, and to find correlations with engine-out particulate matter (PM) levels, see Figure 2 Φ at the lift-off position does not significantly correlate with engine-out PM, i.e. it does not explain the observed variations in PM. High correlation coefficients between PM and; portion of heat release after end of injection (EOI), engine out UHC and engine out CO all suggests that the soot oxidation process may be a more important factor. The F label on the abscissa in Figure 2 refers to a Φ value at a fix position from the injector orifice.

Figure 2. Correlation Coefficients between engine-out PM and different parameters

Ulf AronssonPhD Student

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Studies of Cold Start in a Light-Duty DI Diesel EngineClément Chartier

Light duty diesel engines have evolved tremendously in the past decade to meet new emission legislations. In order to drastically reduce nitrous oxides and soot emissions, the trend has been to use lower compression ratios. This way has been successful for emission reduction during emission cycles. This evolution leads to challenges in term of cold starting since combustion instability and potential for load increase are becoming problematic. The present study investigates cold start at very low temperatures, down to -29 deg C. The experiments were conducted in an optical light duty diesel engine using a Swedish class 1 environmental diesel. In-cylinder imaging of the natural luminescence using a high speed video camera was performed to get a better understanding of the combustion at very low temperature conditions.

The optical engine is based on the Volvo D5 engine. The piston is made of quartz glass, making it possible to conduct optical observations with a realistic combustion chamber design. The engine was modified to perform in cold start conditions. Inlet air, fuel and coolant were cooled down to very low temperatures using a freezer and heat exchangers.

Combustion in cold starting conditions was found to be asymmetrically distributed in the combustion chamber. Combustion was initiated close to the glow plug first and then transported in the swirl direction to the adjacent jets. Figure 1 and Figure 2 illustrate the difference between start at ambient and cold conditions with the same injection strategy. It appears clearly the in the cold start conditions, the combustion starts in the spray close to the glow plug positioned in the upper part of the images. The combustion location is then slightly transported in the combustion chamber following the swirl motion. The fuel evaporation process requires heat from the surrounding air. Therefore, in cold conditions, most of the fuel does not evaporate and take heat from the starting combustion. This makes it difficult for the combustion to fully develop.

Different injection strategies were investigated in order to overcome the limited fuel evaporation process at very low temperatures. Pilot injections and appropriate repartition of the fuel quantity between the different injections gave a more homogeneous combustion. The natural luminescence was symmetrically distributed in the piston bowl and all the jets contributed to the combustion. Significant improvements in combustion stability, load level and potential for load increase were observed as well.

Figure 1. High speed video sequence of a combustion event for ambient conditions. Images from 3 CAD BTDC to 28 CAD ATDC with one image per crank angle degree.

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Figure 2. High speed video sequence of a combustion event for cold starting conditions. Images from 3 CAD BTDC to 28 CAD ATDC with one image per crank angle degree.

Formaldehyde and CO measurements Johan Sjöholm, Elias Kristensson

The following results are taken from the ongoing pre-study for work aimed at identifying sources of HC emissions in a combustion engine. One approach is to locate rich and lean zones in space and time during the combustion event..

The concept that formaldehyde is a good tracer for low temperature reactions in diesel engines is well known. Formaldehyde is formed as part of the primary fuel decomposition. The formaldehyde is then consumed during the high temperature reactions.

However, if a certain region in the engine is over lean the high temperature reactions can fail to consume the formaldehyde leaving a rest of formaldehyde far into the expansion stroke indication over lean zones in the combustion.

A problem associated with this diagnostic is that at the same laser wavelength that excites formaldehyde also excites larger poly aromatic hydrocarbons (PAH). This results in problem regarding analysis as the origin of the two similar signals can not be distinguished easily. The solution could be to use two lasers. The excitation of Formaldehyde exhibit clear line structure that allows for positioning one laser on and one slightly off a formaldehyde absorption line. PAH on the other hand have wide excitation bands that will be excited by both lasers. Thus, taking the differences between the two images isolates the formaldehyde signal.

Bellow are two emission spectrums taken in a Bunsen flame. The dye laser is operated with the dye Pyridine 1 pumped with 532 nm from a Nd:YAG laser resulting in radiation around 708 nm that is then frequency doubled to 354 nm giving about 4 mJ. The dye laser is tuned on and off an excitation line around 354.0 nm. The band structure from formaldehyde is clearly seen in the on-line measurement. Note that the signal is not zero in the off line measurement due to PAH.

Clément Chartier PhD Student

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Figure 1. Formaldehyde spectra taken in a Bunsen flame. The laser is tuned on and off an excitation line around 354.0 nm.

CO on the other hand is a good indicator for rich combustion. A rich region will render the oxidation process of CO incomplete and thus leaving behind CO in to the expansion stroke.

The problem with CO LIF is that it is a two photon process using 230,1 nm laser radiation. This makes the signal extremely week. In addition CO LIF is sensitive to pressure quenching. Thus it is impossible to measure at the elevated pressure close to TDC but it might still be possible to measure later during the expansion stroke.

In order to perform CO LIF a dye laser was specially modified for the task. 355 nm radiation from the third harmonic from a Nd:YAG was used as a pump source. The dye was Coumarin 460 resulting in radiation around 460 nm that was frequency doubled to 230 nm in order to excite the two photon transition in CO. The output energy in 230 nm was around 6 mJ giving more than sufficient signal at room temperature and pressur. Bellow is an emission spectra acquired from a cell containing CO-gas. The excitation wavelength is 230.1 nm and the energy is around 5 mJ.

However, also CO suffers from interference from other species. In this case it is C2 from mainly soot that is excited with the same wavelength. The solution is again to tune the laser on and off the CO excitation wavelength as the C2 excitation is broadband.

Combining Formaldehyde and CO LIF and in particular on / off line measurements of both species at the same time can provide much new information on lean and rich zones in the combustion. Combining these measurements with emission measurements is of course required for increased understanding. In order to pump four dye lasers at the same time the Multi:YAG laser system together with the multi dye system is required. The equipment will be transferred to the engine test bed for in-cylinder measurements during the spring 2009.

Johan SjöholmPhD Student

Elias KristenssonPhD Student

Figure 2. CO emission spectra acquired from a cell containing CO-gas. The excitation wavelength is 230.1 nm.

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Publications and patents

Publications

Dissertations

Håkan Persson, Spark assisted compression ignition : SACI, Ph.D. Thesis, Dept of Energy Sciences, Lund University, Sweden, 2008, Series: Division of Combustion Engines, Department of Energy Sciences, Faculty of Engineering, Lund University, Sweden, 08/1063

Mehrzad Kaiadi, Diluted Operation of a Heavyduty Natural Gas Engine, Ph.D. Thesis, Dept of Energy Sciences, Lund University, Sweden, 2008, Series: Division of Combustion Engines, Department of Energy Sciences, Faculty of Engineering, Lund University, Sweden

Rixin Yu, ”Large Eddy Simulation of Turbulent Flow and Combustion in HCCI Engines”, Ph.D. Thesis, Dept of Energy Sciences, Lund University, May 2008.

Uwe Horn, The Influence of Fuel Properties on CI-Combustion, Ph.D. Thesis, Dept of Energy Sciences, Lund University, Sweden, 2008, Series: Division of Combustion Engines, Department of Energy Sciences, Faculty of Engineering, Lund University, Sweden

Articles and papers

Anders Widd, Per Tunestål, Carl Wilhelmsson, Rolf Johansson, ”Control-Oriented Modeling of Homogeneous Charge Compression Ignition incorporating Cylinder-Wall Temperature Dynamics”, Proc. 9th International Symposium on Advanced Vehicle Control (AVEC’08), Kobe, Japan, October 6-9, 2008, pp.146-151

Anders Widd, Per Tunestål, Carl Wilhelmsson, Rolf Johansson, ”Physical Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines”, Proc. 47th IEEE Conference on Decision and Control, Cancun, Mexico, Dec. 9-11, 2008, pp. 5615-5620

Andreas Vressner, Rolf Egnell, Bengt Johansson, ”Combustion Chamber Geometry Effects on the Performance of an Ethanol Fueled HCCI Engine”, SAE paper 2008-01-1656

Carl Magnus Lewander, Bengt Johansson, Per Tunestal, Nathan Keeler, Nebojsa Milovanovic, Simon Tullis, Par Bergstrand, ” Evaluation of the Operating Range of Partially Premixed Combustion in a Multi Cylinder Heavy Duty Engine with Extensive EGR”, SAE paper 2009-01-1127

Carl Wilhelmsson, Anders Widd, Per Tunestål, Rolf Johansson, Bengt Johansson, ”A Physical Two-Zone NOx Model Intended for Embedded Implementation”, SAE paper 2009-01-1509

Clément Chartier, Ulf Aronsson, Öivind Andersson, Rolf Egnell, Robert Collin, Hans Seyfried, Mattias Richter, and Marcus Aldén, ”Analysis of Smokeless Spray Combustion in a Heavy-Duty Diesel Engine by Combined Simultaneous Optical Diagnostics”, SAE Technical Paper 2009-01-1353 (2009)

Daniel Blom, Maria Karlsson, Kent Ekholm, Per Tunestål and Rolf Johansson, ”HCCI Engine Modeling and Control Using Conservation Principles”, SAE Technical Paper 2008-01-0789

Håkan Persson, Johan Sjöholm, Elias Kristensson, Bengt Johansson, Mattias Richter, J. Bengtsson, Petter Strandh, Rolf Johansson, Per Tunestål, and Bengt Johansson, Hybrid Modelling of Homogeneous Charge Compression Ignition (HCCI) Engine Dynamics - A Survey, International Journal of Control, 2007, Vol. 80, No. 11, pp. 1814-1848

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Kent Ekholm, Maria Karlsson, Per Tunestål, Rolf Johansson, Bengt Johansson, Petter Strandh, ”Ethanol-Diesel Fumigation in a Multi-Cylinder Engine”, SAE World Congress, SAE Technical Paper 2008-01-0033, Detroit, MI, April 2008

Rixin Yu, ”Large Eddy Simulation of Turbulent Flow and Combustion in HCCI Engines”, Dept of Energy Sciences, Lund University, May 2008

Rixin Yu, Tobias Joelsson, Xue-Song Bai, Bengt Johansson, ”Effect of Temperature Stratification on the Auto-ignition of Lean Ethanol/Air Mixture in HCCI engine”, SAE 2008-01-1669; Presented orally at 2008 SAE International Powertrains, Fuels and Lubricants Congress; Shanghai, Peoples Republic of China 23-25 June 2008

Ryo Hasegawa, Ichiro Sakata, Hiromichi Yanagihara, Marcus Alden, Bengt Johansson, ”Quantitative Analysis of the Relation between Flame Structure and Turbulence in HCCI Combustion by Two-Dimensional Temperature Measurement”, SAE paper 2008-01-0061

Sasa Trajkovic, Per Tunestål and Bengt Johansson, ”Investigation of Different Valve Geometries and Valve Timing Strategies and their Effect on Regenerative Efficiency for a Pneumatic Hybrid with Variable Valve Actuation”, SAE Technical Paper 2008-01-1715, Shanghai, China, 2008

Sasa Trajkovic, Per Tunestål, Bengt Johansson,” Simulation of a Pneumatic Hybrid Powertrain with VVT in GT-Power and Comparison with Experimental Data”, SAE paper 2009-01-1323

Thomas Johansson, Bengt Johansson, Per Tunestal, Hans Aulin, ”HCCI operating range in a turbocharged multi cylinder engine with VVT and spray-guided DI” SAE paper 2009-01-0494

Tobias Joelsson, Rixin Yu, Xue-Song Bai, Andreas Vressner, Bengt Johansson, ”Large eddy simulation and experiments of the auto-ignition process of lean ethanol/air mixture in HCCI engines”, SAE 2008-01-1668 Presented orally at 2008 SAE International Powertrains, Fuels and Lubricants Congress; Shanghai, Peoples Republic of China 23-25 June 2008

Ulf Aronsson, Clément Chartier, Johan Sjöholm, Öivind Andersson, Rolf Egnell, Mattias Richter, and Marcus Aldén, ”Analysis of the Correlation Between Engine-Out Particulates and Local Equivalence Ratio in the Lift-Off Region of a Heavy Duty Diesel Engine Using Raman Spectroscopy”, SAE Technical Paper 2009-01-1357

Ulf Aronsson, Clement Chartier, Uwe Horn, Oivind Andersson, Bengt Johansson, Rolf Egnell , ”Heat Release Comparison Between Optical and All-Metal HSDI Diesel Engines”, SAE paper 2008-01-1062

Ulf Aronsson, Clément Chartier, Uwe Horn, Öivind Andersson, Bengt Johansson, and Rolf Egnell, ”Heat Release Comparison Between Optical and All-Metal HSDI Diesel Engines”, SAE Technical Paper 2008-01-1062

Uwe Horn, Erik Rijk, Rolf Egnell, Oivind Andersson, Bengt Johansson, ” Investigation on Differences in Engine Efficiency with Regard to Fuel Volatility and Engine Load” SAE paper 2008-01-2385

Uwe Horn, Håkan Persson, Rolf Egnell, Öivind Andersson, Erik Rijk ”The influence of Fuel Properties on Transient Liquid-Phase Spray Geometry and on CI-Combustion Characteristics”. Submitted to SAE International Powertrains, Fuels and Lubricants meeting, November 2-5 in San Antonio, USA.

Vittorio Manente, Bengt Johansson, Per Tunestal, ”Characterization of Partially Premixed Combustion with Ethanol: EGR sweeps, Low and Maximum Loads”, ASME, ICES 2009, April, paper number: 2009 76165

Vittorio Manente, Bengt Johansson, Per Tunestal,”Half Load Partially Premixed Combustion, PPC, with High Octane Number Fuels. Gasoline and Ethanol Compared with Diesel, ARAI India, January 2009, Paper number: SIAT 2009 295

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Vittorio Manente, Per Tunestål, Bengt Johansson, ” A Novel Model for Computing the Trapping Efficiency and Residual Gas Fraction Validated with an Innovative Technique for Measuring the Trapping Efficiency” SAE paper 2008-32-0003

Vittorio Manente, Per Tunestål, Bengt Johansson, ” Influence of the Wall Temperature and Combustion Chamber Geometry on the Performance and Emissions of a Mini HCCI Engine Fuelled with DEE”, SAE paper 2008-01-0008

Vittorio Manente, Per Tunestål, Bengt Johansson, ” Validation of a Self Tuning Gross Heat Release Algorithm”, SAE paper 2008-01-1672

Vittorio Manente, Per Tunestål, Bengt Johansson, ”Partially Premixed Combustion at High Load using Gasoline and Ethanol, a Comparison with Diesel”, SAE paper 2009-01-0944

PatentsTunestaal, P., Self Tuning Cylinder Pressure Based Heat Release Computation, Worldwide Patent number WO2008095569, August, 2008

ReferencesChapter 4. Combustion Modeling Project

[1] Vressner, A., Hultqvist, A., Johansson, B., ” Study on Combustion Chamber Geometry Effects in an HCCI Engine using High-Speed Cycle-Resolved Chemiluminescence Imaging”. SAE 2007-01-0217.

[2] Seyfried, H., Olofsson, J., Sjöholm, J., Richter, M. Aldén M., Vressner, A., Hultqvist, B. and Johansson, B., “High-Speed PLIF Imaging for Investigation of Turbulence on Heat Release Rates in HCCI Combustion”, SAE 2007-01-0213.

[3] Persson H., Hultqvist A., Johansson B. and Remón A. (2007) Investigation of the Early Flame Development in Spark Assisted HCCI Combustion Using High Speed Chemiluminescence Imaging SAE paper: 2007- 01-0212

[4] Persson H. (2008) Spark Assisted Compression Ignition SACI, Doctoral Thesis, Lund University.

[5] Marinov, N. M, “A Detailed Chemical Kinetic Model for High Temperature Ethanol Oxidation” Int. J. Chem. Kinet. 31:183-220 (1999).

Chapter 7. Generic Diesel Project

1. Akihama, K., Takatori, Y., Inagaki, K., Sasaki, S., and Dean, A. M., Mechanism of the Smokeless Rich Diesel Combustion by Reducing Temperature, presented at SAE World Congress, 2001-01-0655, 2001

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KCFPKompetenscentrum Förbränningsprocesser

Centre of Competence Combustion ProcessesFaculty of Enginering, LTH

P.O. Box 118SE-221 00 Lund

Sweden