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HCCI EngineHCCI Engine

HOMOGENEOUS CHARGE HOMOGENEOUS CHARGE COMPRESSION IGNITION COMPRESSION IGNITION ENGINEENGINE

CONTENTS1. HISTORY

2. DEFINITION

3. HCCI & OTHERS

4. SI , CI & HCCI

5. PRINCIPLE

6. HCCI CONCEPT

7. OPERATION METHODS

8. CONTROL OF HCCI

9. ADVANTAGES

10. DIS- ADVANTAGES

11. CHALLENGES

12. FUTURE OF HCCI

13. CONCLUDING REMARKS

HISTORY HCCI engines have a long history,

even though HCCI has not been as

widely implemented as spark ignition

or diesel injection.

HOT-BULB ENGINE

In fact, HCCI was popular before electronic spark ignition was used. One example is the HOT-BULB ENGINE .Another example is the “DIESEL” MODEL AIRCRAFT ENGINE.

DEFINITION

• Homogeneous charge compression ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition.

• HCCI has characteristics of the two most popular forms of combustion used in SI engines: spark ignition (gasoline engines) and CI engines: compression ignition (diesel engines).

HCCI & others

• In SI , the fuel and oxidizer are mixed together and an electric discharge is used to ignite a portion of the mixture.

• CI also relies on temperature and density increase resulting from compression, but combustion occurs at the boundary of fuel-air mixing, caused by an injection event, to initiate combustion.

• However in HCCI , rather than using an electric discharge to ignite a portion of the mixture, the density and temperature of the mixture are raised by compression until the entire mixture reacts spontaneously and auto-ignites.

SI Engine HCCI

SI , CI and HCCI

Traditional combustion (left) uses a spark to ignite the mixture. HCCI Traditional combustion (left) uses a spark to ignite the mixture. HCCI (right) uses piston compression for a more complete ignition.(right) uses piston compression for a more complete ignition.

SI , CI & HCCI

• In SI & CI, the combustion occurs in a flame front and only a portion of the air-fuel mixture burns at a time.

• In HCCI, combustion initiates simultaneously at multiple sites within the combustion chamber and there is no discernable flame propagation.

HCCI CONCEPT

OPERATION METHODS• Fuel-air will ignite when the conc. and temp. of reactants is

sufficiently high. It can be increased by :

High compression ratio

Pre-heating of induction gases

Forced induction

Retained or re-inducted exhaust gases

• Once ignited, combustion occurs very quickly. When auto-ignition occurs too early or with too much chemical energy, combustion is too fast and high in-cylinder pressures can destroy an engine. For this reason, HCCI is typically operated at lean overall fuel mixtures.

CONTROL OF HCCI

• In an HCCI engine, the homogeneous mixture of fuel and air is compressed and combustion begins whenever the appropriate conditions are reached. This means that there is no well-defined combustion initiator that can be directly controlled.

• Engines can be designed so that the ignition conditions occur at a desirable timing. To achieve dynamic operation in an HCCI engine, the control system must change the conditions that induce combustion. Thus, the engine must control either the compression ratio, inducted gas temperature, inducted gas pressure, fuel-air ratio, or quantity of retained or re-inducted exhaust.

CONTROL APPROACH

Several control approaches are discussed below.

•Variable compression ratio

•Variable induction temperature

•Variable exhaust gas percentage

•Variable valve actuation

•Variable fuel ignition quality

•Direct Injection: PCCI or PPCI Combustion

ADVANTAGES• HCCI provides up to a 30-percent fuel savings, while

meeting current emissions standards.

• Since HCCI engines are fuel-lean, they can operate at a Diesel-like compression ratios (>15), thus achieving higher efficiencies than conventional SI gasoline engines.

• Homogeneous mixing of fuel and air leads to cleaner combustion and lower emissions. Actually, because peak temperatures are significantly lower than in typical SI engines, NOx levels are almost negligible.

ADVANTAGES

• HCCI is closer to the ideal Otto cycle than spark-ignited combustion.

• Additionally, the premixed lean mixture does not produce soot.

• HCCI engines can operate on gasoline, diesel fuel and most alternative fuels.

• Since HCCI runs throttle less, it eliminates throttling losses.

DIS-ADVANTAGES• High in-cylinder peak pressures may cause damage to the

engine.

• High heat release and pressure rise rates contribute to engine wear.

• The auto-ignition event is difficult to control, unlike the ignition event in gasoline and diesel engines which are controlled by spark plugs and in-cylinder fuel injectors, respectively.

• CO and HC pre-catalyst emissions are higher than a typical SI engine, caused by incomplete oxidation (due to the rapid combustion event and low in-cylinder temperatures) and trapped gases, respectively.

CHALLENGES

• Controlling Ignition Timing over a Range of Speeds and Load .

• Extending the Operating Range to High Load .

• Cold-Start Capability.

• Unburnt Hydrocarbon and Carbon Monoxide Emission .

THE FUTURE OF HCCI

• The future of HCCI looks promising specially with partial HCCI mode.

• Major companies such as GM, Mercedes-Benz, Honda, and Volkswagen have invested in HCCI research.

• General Motors has demonstrated Opel Vectra and Saturn Aura with modified HCCI engines.

• Mercedes-Benz has developed a prototype engine called DiesOtto, with controlled auto ignition. It was displayed in its F 700 concept car at the 2007 Frankfurt Auto Show.

THE FUTURE OF HCCI• Volkswagen are developing two types of engine for

HCCI operation. Combined Combustion System(CCS); is diesel engine but uses homogenous intake charge rather than traditional diesel injection. Gasoline Compression Ignition(GCI); it uses HCCI when cruising and SI when accelerating. The company expects them to be ready for production in about 2015.

• In October 2005, the Wall Street Journal reported that Honda was developing an HCCI engine as part of an effort to produce a next generation hybrid car.

HCCI ENGINE ON ROAD

CONCLUDING REMARKS• HCCI is a high-risk, long-term alternative technology deserving

of increased support and develpoment.

• HCCI engines have the potential to match or exceed the efficiency of diesel-fueled CIDI engines without the major challenge of NOx and PM emission control or a major impact on fuel-refining capability.

• A high-efficiency, gasoline-fueled HCCI engine represents a major step beyond SIDI engines for light-duty vehicles.

• For heavy-duty vehicles, successful development of the diesel-fueled HCCI engine is an important alternative strategy in the event that CIDI engines cannot achieve future NOx and PM emissions standard.

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