HCCI (Homogeneous Charge Compression Ignition)

HCCI (Homogeneous Charge Compression Ignition)

Aug 29, 2013 No Comments

Background: Homogeneous Charge Compression Ignition (HCCI) also termed as Controlled Auto-Ignition (CAI) is a combustion technology for ICE and a potential future-engine-strategy for automobile companies. HCCI is an alternative piston-engine combustion process that can provide efficiencies as high as compression-ignition, direct-injection (CIDI) engines (an advanced version of the commonly known diesel engine) while, unlike CIDI engines, producing ultra-low oxides of nitrogen (NOx) and particulate matter (PM) emissions. HCCI engines operate on the principle of having a dilute, premixed charge that reacts and burns volumetrically throughout the cylinder as it is compressed by the piston. In some regards, HCCI incorporates the best features of both spark ignition (SI) and compression ignition (CI). As in an SI engine, the charge is well mixed, which minimizes particulate emissions, and as in a CIDI engine, the charge is compression ignited and has no throttling losses, which leads to high efficiency. However, unlike either of these 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.
Many other names have also been used in recognising this potential combustion strategy, such as:

1.Active Thermo-Atmosphere Combustion (ATAC), Activated Radicals (AR) combustion, Compressed air assisted fuel injection process (IAPAC), Toyota-Soken combustion (TS), etc., for two-stroke engines;
2.Homogeneous Charge Compression Ignition (HCCI), Compression Ignited Homogeneous Charge (CIHC) combustion, Premixed Charge Compression Ignition (PCCI), Control Auto-Ignition (CAI) combustion, Diesel combustion under uniform higher-dispersed mixture formation (UNIBUS), etc., for four-stroke engines.
(From SAE paper 2002-01-1923, 2001-01-1890)

Pros and cons in HCCI engine
1. Low fuel consumption
2. Low NOx emission
3. Low soot emission

1.Narrow operating range
2.High in-cylinder peak pressure
3.High HC and CO emission

The technical challenges associated with HCCI development
1.Start of combustio and burn rate control
2.A narrow operating regime
3.A lower power density
4.Difficulty in operation at higher loads
5.Excess rate of heat release leading to high combustion noise level and possible engine damage, particularly at higher loads
6.Difficulty during transient operation (operating mode transition)
7.Excess CO and HC emissions, particularly at light load
8.Difficulty with cold start

HCCI combustion in KAIST engine Lab.
The research scope in HCCI combustion is follow;
1. Effect of fuel type
2. Effect of injector location
3. Effect of injection pressure
4. Effect of compression ratio
5. Effect of inlet temperature
6. Effect of valve timing
7. Effect of boosting

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