CRDi Engine

What is CRDi? CRDi stands for Common Rail Direct injection meaning

direct injection of fuel into cylinders of an engine via asingle, common line, called common rail which isconnected to all fuel injectors .

Instead of supplying separate piston pumps for fuel supply, the common rail alone supplies high pressure fuel to eachcylinder.

Disadvantages of Diesel Engine They were cam driven, and injection pressure was proportional to engine

speed. This typically meant that the highest injection pressure could only be achieved at the highest engine speed and the maximum achievable injection pressure decreased as engine speed decreased. This relationship is true with all pumps, even those used on common rail systems; with the unit or distributor systems, however, the injection pressure is tied to the instantaneous pressure of a single pumping event with no accumulator, and thus the relationship is more prominent and troublesome.

They were limited in the number and timing of injection events that could be commanded during a single combustion event. While multiple injection events are possible with these older systems, it is much more difficult and costly to achieve.

The Technology Whereas ordinary diesel direct fuel-injection systems

have to build up pressure anew for each and every injection cycle, the new common rail (line) engines maintain constant pressure regardless of the injection sequence. This pressure then remains permanently available throughout the fuel line.

The engine's electronic timing regulates injection pressure according to engine speed and load. The electronic control unit (ECU) modifies injection pressure precisely and as needed, based on data obtained from sensors on the cam and crankshafts. In other words, compression and injection occur independently of each other. This technique allows fuel to be injected as needed, saving fuel and lowering emissions.

Layout of typical CRDi System

Traditional injection system An auxiliary cam on the engine camshaft drives a single-cylinder injection pump.

Early in the stroke of the plunger, the inlet port is closed and the fuel trapped above the plunger is forced through a check valve into the injection line. The injection nozzle has several holes through which the fuel sprays into the cylinder. A spring-loaded injection needle keeps the injection valve closed until the pressure in the injector volume, acting on parts of the needle surface, overcomes the spring force and opens the valve.

Thus, the phase of the pump camshaft relative to the engine crankshaft controls the start of injection, while the force given by the initial displacement of the spring gives the opening pressure. Injection is stopped when the inlet port of the pump is uncovered by a helical groove in the pump plunger, and thehigh pressure above the plunger and in the injector volume is released. The injection pump cam design and the position of the helical groove determine the amount of fuel injected into the cylinder. Thus for a given cam design, the rotating plunger and its helical groove controls the load.

Traditional injection system

Common rail injection system Contrary to the traditional injection system, pressure generation and

injection are decoupled in the common rail system. A prerequisite for this decoupling of pressure generation and injection in common rail systems is the high-pressure accumulator, which consists of the rail and the high pressure fuel lines to the nozzles.

In order to control the opening and closing time of the needle, a small chamber of pressurised fuel is present at the top of the needle. This volume is connected to the rail through a small orifice that assures that same pressure between the nozzle and the chamber when the valve is closed.

EQUIPMENT SETUP1: fuel tank with low pressure

pump2: fuel filter, 3: high pressure pump4: pressure regulating valve,5: high pressure vessel (rail), 6: fuel injector with solenoid

valve and nozzle, 7: safety valve,8: heat exchanger, 9: control unit, 10: pressure transducer

IGNITION AND COMBUTION

The common-rail fuel injection system produces droplets of less than 20Mm, which evaporate rapidly. This led to a short ignition delay and a continued combustion of the fuel during the injection. Therefore, together with pilot injection, a significant reduction of the ignition delay of the main injection can be realized, especially when the fuel jet of the main injection penetrates through the flame of the pilot injection.

Common Rail System it is conceivable to apply up to pilot/post injections for each single compression stroke obtaining acceptable spray properties.

A view of Common rail

COMPARISSION BETWEEN NORMAL ENGINE & CRDI ENGINE

Normal Diesel Engine CRDI engine

Pressures ranging from 200 - 400 bar Pressures exceeding 1200 bar, uniformly maintained

Indirect injection of fuel Direct injection of high pressure fuel

Noisy engine Less engine noise (Pilot injection prior to main

injection.

Fuel injection pressure varies during the Injection

Pump & variable with

Engine speed

Fuel injection timing mechanically controlled by Fuel

High fuel consumption at low engine speed (due to

imperfect air-fuel ratio)

High emission at low engine speed Low emission at all engine speeds

Used in normal cars. Used in Hundai i30

ADVANTEGES More power is developed. Increased fuel efficiency. Reduced noise. More stability. Pollutants are reduced. Particulates of exhaust are reduced. Exhaust gas recirculation is enhanced. Precise injection timing is obtained. Pilot and post injection increase the combustion quality. More pulverization of fuel is obtained. A very high injection pressure can be achieved.

DISADVANTAGE The main disadvantge is the cost of the engine. It is costly than conventional

engines.

APPLICATIONS Marine & Locomotive engines Following car manufacturers applied the CRDi system:

Ashok Leyland's CRS Engines (used in U Truck and E4 Busses) BMW's D-engines (also used in the Land Rover Freelander TD4) Chevrolet's VCDi (licensed from VM Motori) Fiat Group's (Fiat, Alfa Romeo and Lancia) JTD (also branded as MultiJet, JTDm, Ecotec

CDTi, TiD, TTiD, DDiS, Quadra-Jet) Ford Motor Company's TDCi Duratorq and Powerstroke Honda's i-CTDi Hyundai CRDi Mahindra's CRDe Mazda's MZR-CD (1.4 MZ-CD, 1.6 MZ-CD manufactured by joint venture Ford/PSA Peugeot Citron) and

earlier DiTD Mitsubishi's DI-D (recently developed 4N1 engine family uses next generation 200 MPa (2000 bar) injection system)) Nissan's dCi, Infiniti uses dCi engines, but not branded as dCi. Opel's CDTI Proton's SCDi PSA Peugeot Citron's HDI or HDi (1.4HDI, 1.6 HDI, 2.0 HDI, 2.2 HDI and V6 HDI developed under joint venture

with Ford)

REFERENCESWebsites:http://en.wikipedia.org/w/index.php?title=Common_raihttp://www.thegeminigeek.com/what-is-a-crdi-engine/http://en.wikipedia.org/w/index.php?title=Hyundai_i30http://seminarprojects.com/Thread-common-rail-direct-injection-crdi-engines--1368

Books:Internal Combustion Engines By: Anand V Domkundwar.Thermal Engineering by R.S.Khurmi

Conclusion

From learning about the CRDi ttechnology I hereby concludde that it is a revolutionary technology as it makes the engine 33% more efficient than the ordinary fuel injection system

Slide Number 1What is CRDi?Disadvantages of Diesel EngineThe TechnologyLayout of typical CRDi SystemTraditional injection systemSlide Number 7Slide Number 8Slide Number 9IGNITION AND COMBUTIONSlide Number 11COMPARISSION BETWEEN NORMAL ENGINE & CRDI ENGINEADVANTEGES DISADVANTAGEAPPLICATIONSREFERENCESConclusion