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C Kannan et. al. / International Journal of Engineering Science and Technology

Vol. 2(8), 2010, 3525-3534

EXPERIMENTAL INVESTIGATION OF

COMBUSTION, PERFORMANCE AND

EMISSION CHARACTERISTICS OF DIDIESEL ENGINE UNDER HCCI MODE

WITH POROUS MEDIUM COMBUSTION

C KANNAN*

Department of Automobile Engineering, Sri Venkateswara College of Engineering,

Post Bag No.3, Pennalur, Sriperumbudur, Tamilnadu 602 105, India

P TAMILPORAI

Division of IC Engines, Department of Mechanical Engineering, College of Engineering, Guindy

Anna University, Chennai, Tamilnadu- 602 105, India

Abstract:In recent times, homogeneous combustion has been a proven technology to attain high efficient and low emission

engines. Homogenous Charge Compression Ignition (HCCI) engines are able to have efficiencies as high as

Compression Ignition, Direct Injection (CIDI) engines, while producing ultra-low emissions of nitrogen oxides

(NOx) and particulate matter (PM).HCCI combustion is achieved by controlling the temperature, pressure and

composition of the fuel-air mixture so that it spontaneously gets ignited in the combustion chamber. Numerous

techniques such as Variable Exhaust Gas Recirculation (VEGR), Variable Compression Ratio (VCR) and Variable

Valve Timing (VVT) have been proposed to control the homogeneous combustion inside the engine cylinder. Even

though these techniques are attractive and having good time response, they are too expensive to afford. This paper

investigates the performance, combustion and emission characteristics of a Direct Injection (DI) diesel engine under

HCCI mode which is established through an effective and affordable technique called Porous Medium Combustion

(PMC).

Keywords: homogeneous combustion; porous medium combustion; particulate matter; nitrogen oxides.

1. IntroductionReduction in diesel engine emissions, in particular NOx and PM emission is becoming as high priority issue as

emission norms are getting more and more stringent now a days. The rigid emission standards urged the engine

researchers to innovate techniques that produce high efficient and low emission engines. One such novel technique

is HCCI combustion. Moreover, this technique can be scaled to virtually every size-class of transportation engines

from small motorcycle to large ship engines [U.S congress report, (2001)]. The operational control of an HCCI

engine over a wide range of speeds and loads is probably the most difficult hurdle. HCCI engine ignition is largely

determined by the charge mixture composition, its time-temperature history and to a lesser extent pressure. Althoughit has been demonstrated that HCCI engines operate well at low to medium loads, severe complications have been

observed at high loads. At higher loads, the combustion becomes more rapid which subsequently leading to intense

mechanical noise, engine damage and unacceptable levels of NOx emissions.

Preliminary research indicates that the operating range of HCCI engines can be extended significantly by

partially stratifying the fuel-air charge/ residual charge at high loads. The potential mechanisms for achieving partial

charge stratification include: in-cylinder fuel injection, water injection, varying the intake and in-cylinder mixing

processes and altering in-cylinder flows to vary heat transfer. Due to the difficulties being faced at higher loads,

HCCI engines are generally designed to switch over to conventional Spark Ignition (SI) or Compression Ignition

(CI) mode of combustion at this operational region [Weclas (2004a)].

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An experimental technique which inherits the positive aspects of HCCI combustion at low to medium loads and

concurrently keeps away from the negative attributes of HCCI combustion at higher loads is the matter of immediate

concern. Based on literature survey [Chidambaram (2009) and Weclas (2004b)], homogeneous combustion

established through porous medium combustion technique (HCCI-PMC) has been attempted in this experimental

investigation. In this study, PMC technique has been implemented on a single cylinder, direct injection diesel

engine. It has been found that this technique is able to produce relatively high efficiency and low particulate

emissions from a diesel engine. Low NOx

emission than HCCI mode is the added advantage of this technique [Jan

(2001), Wang (2000) and Afsharvahid(2007)].

In the initial stage, the conventional engine was operated without any modifications. In the second stage, the

engine was made to run in HCCI mode, established through the combination of technologies such as high pressure

fuel injection, injection timing advance, pre-heating the air of induction manifold and cooled exhaust gas

recirculation. The performance, combustion and emission characteristics of the engine under this mode were

recorded. In the third stage, a ceramic material with large porosity was introduced into the combustion chamber of

the engine to accomplish HCCI-PMC. Then the experiments were conducted and the readings were taken. As an end

note, the combustion, performance and emission characteristics of engine under different modes of combustion such

as Conventional, HCCI and HCCI-PMC were compared and presented in this paper.

2. Experimental SetupGenerally, the porous medium combustion can be achieved by the precise placement of porous ceramic material

in either of the following locations: cylinder, engine head or piston. In this research work, the porous ceramicmaterial was placed on the top of piston cavity and had been detained in its position through an appropriate locking

mechanism. The inherent physical and thermal characteristics of porous ceramic material was utilized for the fast

and complete evaporation of the liquid fuel while large porosity characteristic being utilized for proper mixing with

air and volumetric combustion. The photographic view of such a piston with porous medium implementation was

shown in Fig. 1.The chemical composition and mechanical properties of porous ceramic material were given in

Table 1.

Fig. 1.Photographic view of piston with porous medium implementation

Table 1. Properties of porous ceramic material

Molecular

formula

Density (g/m3) Solubility in

water

Melting point

(0 C)

Boiling point

(0 C)

ZrO2 5.89 Negligible 2715 4300

A single cylinder four stroke direct injection air-cooled diesel engine, most commonly used for agricultural

applications in India, was used for the experimental investigation. The specifications of this engine were given in

Table 2. The schematic diagram of the experimental set-up was shown in Fig. 2. The engine was coupled to an

electrical dynamometer to provide the brake load. The fuel consumption was measured with the aid of a glass

burette and stopwatch on volume basis. A Piezo-electric pressure transducer (GH12D Miniature Pressure

Transducer) coupled with an angle encoder was used to measure the combustion chamber pressure with respect to

crank angle. The setup was connected to a personal computer with AVL engine evaluation software. Five-gas

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exhaust analyzer was used to determine the emissions of CO (carbon monoxide), CO2 (carbon dioxide), HC

(hydrocarbon) by infra-red measurement and NOx (nitrogen oxides) by electrochemical sensors. Smoke intensity

was measured with an AVL 415 smoke meter.

Table 2 Specifications of experimental engine

Make Kirloskar

Model TAF 1

Bore Stroke (mm) 87.5 110

Compression ratio 17.5:1

Cubic capacity 0.661 litres

Rated power 4.4 KW

Table 2 (Continued)

Rated speed 1500 rpm

Start of injection 23.4 bTDC

Connecting rod length 220 mm

Injector operating pressure 200 205 bar

1 - Diesel engine 2 - Electrical dynamometer 3 Dynamometer controls

4 Air box 5 U-tube manometer 6 Fuel tank

7 Fuel measurement 8 Pressure transducer 9 TDC position sensor

10 Charge amplifier 11 TDC amplifier circuit 12 Analog to digital card

13 Computer 14 Exhaust gas analyzer 15 AVL smoke meter

16 Air preheater 17 EGR control valve

Fig. 2. Schematic layout of experimental set-up

3. Results and DiscussionIn this research work, an attempt has been performed to compare the combustion and performance

characteristics of a DI diesel engine under conventional, HCCI and HCCI-PMC modes of combustion.

3.1.Combustion characteristics3.1.1.Ignition delay

The variation of ignition delay with brake power for different modes of combustion was shown in Fig. 3. It was

inferred that ignition delay started to decrease with an increase in brake power for almost all modes of combustion.

With an increase in brake power, the amount of fuel being burnt inside the cylinder gets increased and subsequently

1

2

54

6

714

15 3

12

8

9

10

11

13

16

17

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the temperature of in- cylinder gases gets increased. This may lead to reduced ignition delay in all modes of

combustion. However, the ignition delay for diesel fuel was lower under HCCI and HCCI-PMC modes than the

conventional combustion mode. It was evident that the ignition delay was lowest in HCCI-PMC mode from medium

to high load. This might be due to the positive influence of hot porous medium on the evaporation of liquid fuel and

its mixing with air.

13.5

14

14.5

15

15.5

16

16.5

17

0 1.1 2.2 3.3 4.4Brake power in kW

IgnitiondelayindegC

Conventional

HCCI

HCCI-PMC

Fig. 3. Variation of ignition delay for different modes of combustion

3.1.2. Peak pressure

The variations of peak cylinder gas pressure with brake power for different modes of combustion were given in

Fig. 4. It was observed that the peak pressure gets increased with an increase in brake power. During measurements,

the maximum peak pressure under HCCI mode and lowest peak pressure under conventional combustion mode wereobserved. In a conventional direct injection diesel engine, at any point of time, only a fraction of total injected fuel

was getting burnt. But on the other hand, under HCCI combustion mode, the entire fuel-air mixture got ignited and

also burnt simultaneously (volumetric combustion). This might be leading to highest peak pressure in HCCI mode.

However, in HCCI-PMC mode, the magnitude of peak pressure was slightly lower than HCCI, which might be due

to pressure drop across the pores of ceramic medium placed inside the combustion chamber.

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53

55

57

59

61

63

65

67

69

71

73

0 1.1 2.2 3.3 4.4Brake Power in kW

Peakpressureinb

ar

Conventional

HCCI

HCCI-PMC

Fig. 4. Variation in peak pressure for different modes of combustion

3.1.2.Heat release rate

The heat release rate at different crank angles at rated load for different modes of combustion was shown in

Fig. 5.It was inferred that the heat release patterns of all combustion modes were similar but with slight variations. It

was observed that the heat release pattern was rapid and intense in HCCI mode combustion. In HCCI-PMC mode,

even though the heat release rate was more rapid than the conventional combustion mode; the heat was released in a

controlled manner.

-10

0

10

20

30

40

50

60

70

80

90

-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12

Crank angle in degrees (aTDC)

RateofheatreleaseinJ/degCA

Conventional

HCCI

HCCI-PMC

Fig. 5. Rate of heat release pattern for different modes of combustion

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3.2.Performance Characteristics3.2.1 Specific fuel consumption

0

0.1

0.2

0.3

0.4

0.5

0.6

0.0 1.1 2.2 3.3 4.4Brake power in kW

Specificfuelconsumptioning/kW

-hr

Conventional

HCCI

HCCI-PMC

Fig. 6. Comparison of specific fuel consumption for different modes of combustion

The variation in specific fuel consumption against brake power for different modes of combustion was shown

in Fig. 6. It was inferred that the specific fuel consumption was lower in the case of HCCI and HCCI-PMC, as thesemodes were predominately operated with a dilute homogeneous charge. Even within these two modes, HCCI-PMC

had superior characteristics over HCCI mode, which might be due to enhanced evaporation and mixing of fuel with

air by the presence of hot porous medium.

3.2.2Brake thermal efficiency

From Fig 7, it was inferred that the brake thermal efficiencies were increasing with an increase in brake powerfor all modes of combustion that were under consideration. Even though the brake thermal efficiencies did not vary

too much between HCCI and HCCI-PMC modes, these modes were found to offer better thermal efficiencies than

the conventional combustion mode. This might be due to the enhanced evaporation and mixing rate in the case of

HCCI-PMC mode of combustion.

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0

5

10

15

20

25

30

0.0 1.1 2.2 3.3 4.4Brake power in kW

Brakethermalefficiencyin%

Conventional

HCCI

HCCI-PMC

Fig. 7. Comparison of brake thermal efficiency for different modes of combustion

3.3.Emission Characteristics3.3.1 Unburned hydrocarbons (UBHC)

0

5

10

15

20

25

30

0.0 1.1 2.2 3.3 4.4

Brake power in kW

Unburnedhydroca

rbonsinpp

Conventional

HCCI

HCCI-PMC

Fig. 8. Comparison of hydrocarbon emissions for different modes of combustion

The comparison of unburned hydrocarbon emissions in a DI diesel engine with different modes of combustion

was presented in Fig. 8. HC emissions were significantly higher for HCCI and HCCI-PMC modes. Since HCCI

operates on lean mixtures, the peak temperatures were lower in comparison to a conventional diesel engine. These

low peak temperatures might be leading to incomplete burning of fuel, especially near the walls of the combustionchamber, which was one of the possible reasons for higher HC emissions in these modes. However HC emissions

were lower in HCCI-PMC over HCCI mode. This might be due to later stage oxidation of HC compounds inside the

hot porous medium.

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3.3.2 Carbon monoxide (CO)

0

0.05

0.1

0.15

0.2

0.25

0.0 1.1 2.2 3.3 4.4

Brake power in kW

Carbonmonoxidein

Conventional

HCCI

HCCI-PMC

Fig. 9. Comparison of carbon monoxide emissions for different modes of combustion

The comparison of carbon monoxide emissions in a DI diesel engine with different modes of combustion was

presented in Fig. 9. Carbon monoxide emissions were also higher for HCCI and HCCI-PMC modes. However,carbon monoxide emissions were lower in HCCI-PMC mode than HCCI mode under low to medium loads. Surplus

oxygen availability and the presence of hot porous medium might promote later stage oxidation of carbon monoxide

across the combustion chamber, which consequently resulted in lower emissions at these loads.

3.3.3Nitrogen oxides (NOx)

As far as the nitrogen oxide emissions were concerned, it was found to be the lowest in the case of HCCI-PMC mode. This might be due to the heat absorbing characteristics of porous medium which was placed inside the

combustion chamber. Due to this heat absorption from the reaction zone, the in-cylinder temperature was

comparatively lower in HCCI-PMC mode through out the cycle. This consequently resulted in low thermal NOx

emissions. In HCCI mode of combustion, at higher loads, the combustion became more rapid and intense andeventually producing unacceptable levels of NOx emissions. This was shown in Fig. 10.

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150

350

550

750

950

1150

1350

0.0 1.1 2.2 3.3 4.4Brake power in kW

Nitrogenoxidesinpp

Conventional

HCCI

HCCI-PMC

Fig. 10. Comparison of nitrogen oxide emissions for different modes of combustion

3.3.4 Soot

0

50

100

150

200

250

0.0 1.1 2.2 3.3 4.

Brake power in kW

Sootinmg/m3

Conventional

HCCI

HCCI-PMC

Fig. 11. Comparison of soot emissions for different modes of combustion

Due to diluted homogeneous charge in HCCI and HCCI-PMC modes, the soot emissions were found to belower in these modes than the conventional mode of combustion. This was presented in Fig. 11. In HCCI-PMC

mode, the soot emission was higher at low range of part loads due to ineffective evaporation of injected fuel. But

under medium to higher loads in HCCI-PMC mode, the porous medium absorbed heat (from the reaction zone of thecombustion chamber) was utilized for the effective evaporation of liquid fuel and its porosity distribution assisted in

thorough mixing of fuel vapour with air, eventually leading to homogenous mixture which in turn resulted in lowest

soot emission of all modes.

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4. Concluding RemarksThe combustion, performance and emission characteristics of single cylinder DI diesel engine under

conventional, HCCI and HCCI-PMC modes were investigated and summary of the findings were given below.

(1) The ignition delay was found to be lower in HCCI and HCCI-PMC modes due to homogeneous mixture

conditions.(2) Maximum peak gas pressure was observed in HCCI mode; whilst slightly lower peak pressure than HCCI

mode was observed in HCCI-PMC mode due to pressure drop across the porous ceramic medium whichwas placed in the combustion chamber.

(3) The brake thermal efficiencies were higher in HCCI and HCCI-PMC modes than the conventional

combustion mode.

(4) Soot emission under HCCI and HCCI-PMC modes were found to be superior to conventional mode ofcombustion.

(5) The NOx emissions were comparable with conventional mode under low to medium loads. But at high loadunder HCCI mode, the NOx emission was higher due to rapid combustion established through

homogeneous mixture. However, due to heat absorption characteristics of porous medium, the NO x

emission was lower in HCCI-PMC mode when compared to HCCI mode.

(6) HCCI and HCCI-PMC modes had inferior characteristics with respect to HC and CO emissions. But itcould be easily resolved by the use of ultra low light-off temperature oxidation catalysts.

As an end note, this research work would like to conclude that with proper implementations, the HCCI-PMCmode had the potential of offering better combustion, performance and emission characteristics in direct injection

diesel engines.

Acknowledgement

We thank the management of Sri Venkateswara College of Engineering for providing us the necessary

experimental setup to perform this research work.

References

[1] Afsharvahid.S., Ashman.P.J., Dally.B.B.,(2007): Investigation of NOx conversion characteristics in a porous medium, Combustion andFlame, 06, pp.1-12

[2] Kannan Chidambaram, Tamilporai Packirisamy(2009): Smart ceramic materials for homogeneous combustion in internal combustionengines A review, Thermal Science,13 , pp. 153-163

[3] Miroslaw Weclas(2004): Potential of porous medium combustion technology as applied to internal combustion engines, SonderdrunckSchriffenreihe Der Georg- Simon -Ohm Fachhochschule Numberg NR.32, ISSN 1616-0762

[4] Miroslaw Weclas (2004): Strategy for intelligent internal combustion engine with homogeneous combustion in cylinder, SonderdrunckSchriffenreihe Der Georg- Simon -Ohm Fachhochschule Numberg NR.32, ISSN 1616-0762

[5] Macek Jan, Polasek Milos (2001): Porous medium combustion in engines may contribute to lower NOx emissions, Joesef Bozek ResearchCenter, Czech Technical University in Prague, Czech Republic, Paper Code: F02V147

[6] U.S Department of Energy, A Report to US Congress (2001):Homogeneous Charge Compression Ignition (HCCI) Technology[7] Wang.W.G., Lyons.D.W., Clark.N.N.,Gautam.M (2000): Emissions from nine heavy trucks fueled by diesel and biodiesel blend without

engine modification, Environmental Science Technology, 34, pp.933-939

ISSN: 0975-5462 3534

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