Homogeneous Charge Compression Ignition (HCCI) Engines
Contents
Need of HCCI HCCI Engine Concept Advantage & Challenges related to HCCI Future Aspects.
Solution• Hybrid Vehicles• Fuel Cells• HCCI Engines• GDI Engine• Low Emissions Technologies• New Materials• Advanced Design Simulations• Efficient Electronics and Electrical Devices
What is an HCCI Engine?
• HCCI is a form of internal combustion in which the fuel and air are compressed to the point of auto ignition.
• That means no spark is required to ignite the fuel/air mixture
• Creates the same amount of power as a traditional engine, but uses less fuel.
Traditional combustion (left) uses a spark to ignite the mixture. HCCI (right) uses piston compression for a more complete ignition.
How Does It Work?
• A given concentration of fuel and air will spontaneously ignite when it reaches its auto-ignition temperature.
• The concentration/temperature can be controlled several ways:– High compression ratio– Preheating of induction gases– Forced induction– Retaining or reintroducing exhaust
gases
Click here for a nice animation of an HCCI engine in action!
The Challenges Facing Us…
• Emission (NOx & Soot)• Fuel Economy
Fuel Consumption is increased by more than 10 % in last 7 years
Urban Urban PollutionPollution
Traditional combustion (left) uses a spark to ignite the mixture. HCCI (right) uses piston compression for a more complete ignition.
• Unlike conventional engines, the combustion occurs simultaneously throughout the volume rather than in a flame front.
• This important attribute of HCCI allows combustion to occur at much lower temperatures, dramatically reducing engine-out emissions of NOx
SI Engine HCCI
WORKING OF HCCI ENGINE
Comparison with other engines
FOUR STROKE ENGINE
Suction Stroke.
Compression Stroke.
Combustion Stroke.
Exhaust Stroke.
SUCTION STROKE:
Fuel air mixture intake take place.
Compression Stroke: Piston moves from bottom dead centre totop dead centre
COMBUSTION STROKE:
EXHAUST STROKE: Removal of exhaust gases takes place.
Advantages
• Can achieve up to 15% fuel savings
• Lower peak temperature leads to cleaner combustion/lower emissions
• Can use gasoline, diesel, or most alternative fuels
HCCI automobiles could reduce greenhouse gas emissions
POTENTIAL
1. High efficiency, no knock limit on compression ratio..
2. Low PM emissions, no need for PM filter.
3. HCCI provides up to a 15-percent fuel savings, while meeting current emissions standards.
4. HCCI engines can operate on gasoline, diesel fuel, and most alternative fuels.
5. In regards to CI engines, the omission of throttle losses improves HCCI efficiency.
Disadvantages
• Higher cylinder peak pressures may damage the engine
• Auto-ignition is difficult to control
• HCCI Engines have a smaller power range
Prototype HCCI car from Saturn
BARRIERS
1. The auto-ignition event is difficult to control, unlike the ignition event in spark -ignition(SI) and diesel engines which are controlled by spark plugs and in-cylinder fuel injectors, respectively.
2. HCCI engines have a small power range, constrained at low loads by lean flammability limits and high loads by in-cylinder pressure restrictions
3. High HC and CO emissions.
The Future of HCCI
• The future of HCCI looks promising
• Major companies such as GM, Mercedes-Benz, Honda, and Volkswagen have invested in HCCI research.
• Preliminary prototype figures show that HCCI cars can achieve in the area of 43 mpg
HCCI CONCEPT
Starting HCCI engines Charge does not readily auto ignite cold
engines. Early proposal was to start in SI mode
and run in HCCI mode. It involves the risk of knocking and
cylinder failure at high compression ratios.
Now intake air pre-heating with HE and burner system allows startup in HCCI mode with conventional starter.
Control methods of HCCI combustion
The spontaneous and simultaneous combustion of fuel-air mixture need to be controlled.
No direct control methods possible as in SI or CI engines.
Various control methods are:
Variable compression ratio
Variable induction temperature
Variable valve actuation
Control methods of HCCI combustion
Variable compression ratio method
The geometric compression ratio can be changed with a movable plunger at the top of the cylinder head. This concept used in “diesel” model aircraft engine.
Variable induction temperature
The simplest method uses resistance heater to vary inlet temperature. But this method is slow
Now FTM (Fast Thermal Management) is used. It is accomplished by rapidly varying the cycle to cycle intake charge temperature by rapid mixing.
FTM system
Rapid mixing of cool and hot intake air takes place achieving optimal temperature as demanded and hence better control.
Control methods of HCCI combustion Variable valve actuation (VVA)
This method gives finer control within combustion chamber
Involves controlling the effective pressure ratio. It controls the point at which the intake valve closes. If the closure is after BDC, the effective volume and hence compression ratio changes.
Control methods of HCCI combustion
Dual mode transitions
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
This restricts engine operation at high loads
Dual mode transitions Practical HCCI engines will need to
switch to a conventional SI or diesel mode at very low and high load conditions due to dilution limits
Two modes: HCCI-DI dual mode HCCI-SI dual mode
SI mode transitions
It equips VVA and spark ignition system Operates in HCCI mode at low to medium
loads and switches into SI mode at higher loads
Transition is not very stable and smooth
DI-HCCI Long ignition delay and rapid mixing are
required to achieve diluted homogeneous mixture.
Combustion noise and NOx emissions were reduced substantially without an increase in PM.
Combustion phasing is controlled by injection timing.
Thus DI-HCCI proves to be promising alternative for conventional HCCI with good range of operation.
Recent developments in HCCI Turbo charging initially proposed to
increase power Challenges for turbo charging1. Exhaust gas temperatures low (300 to
350 °c) because of high compression ratio.
2. Post turbine exhaust gas temperature must be high enough to preheat intake fuel-air mixture in HE.
3. Low available compressor pressure ratio.
The exhaust has dual effects on HCCI combustion. It dilutes the fresh charge, delaying ignition
and reducing the chemical energy and engine work.
Reduce the CO and HC emissions
Recent developments in HCCI
HCCI prototypes General Motors has demonstrated Opel
Vectra and Saturn Aura with modified HCCI engines.
Mercedes-Benz has developed a prototype engine called Dies Otto, with controlled auto ignition. It was displayed in its F 700 concept car at the 2007 Frankfurt Auto Show
Volkswagen are developing two types of engine for HCCI operation. The first, called Combined Combustion System or CCS, is based on the VW Group 2.0-litre diesel engine but uses homogenous intake charge rather than traditional diesel injection. It requires the use of synthetic fuel to achieve maximum benefit. The second is called Gasoline Compression Ignition or GCI; it uses HCCI when cruising and spark ignition when accelerating. Both engines have been demonstrated in Touran prototypes, and the company expects them to be ready for production in about 2015.
Works Cited• “Homogeneous Charge Compression Ignition”
http://en.wikipedia.org/wiki/Homogeneous_Charge_Compression_Ignition November, 2008.
• “New HCCI Engine” http://videos.howstuffworks.com/multivu/3284-new-hcci-engine-video.htm November, 2008
• “GM Takes New Combustion Technology Out of the Lab and Onto the Road” http://www.gm.com/experience/fuel_economy/news/2007/adv_engines/new-combustion-technology-082707.jsp
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