HCCI engine | Characteristics | Advantages | Disadvantages

HCCI engine full form is Homogeneous charge compression ignition engine.

HCCI is a form of internal combustion in which well-mixed fuel and air are compressed to the autoignition temperature of the fuel.

In the HCCI engine homogeneous mixture is created in the intake system or inside the cylinder. 

Homogeneous charge or air is drawn into the cylinder during suction stroke and compressed to high enough temperature and pressure. To achieve homogeneous spontaneous ignition of the charge preferable near TDC, high intake temperature and the high compression ratio are required. 

After combustion initiation the temperature and pressure rapidly increase and whole bulk of fuel burns simultaneously within a few crank angles. Because the whole mixture burns almost homogeneously unstable flame propagation is avoided. The HCCI non flame combustion process can be described as a ”premixed distributed reaction zone”.

HCCI fast combustion causes very high and fast heat and pressure release. 

Although stable HCCI operation and its substantial benefits have been demonstrated at selected steady-state conditions, several barriers must be overcome before HCCI engine can be widely applied to production automobile and heavy-truck vehicles. 

HCCI provide huge benefits as a future driving propulsion unit to both light and heavy-duty engines.

HCCI is also applicable to be used outside the transportation sector such as those used for electrical power generation. 

HCCI must be operated at very high compression ratios resulting in high efficiency and clean exhaust gases.

Characteristics of the HCCI engine :

• Homogeneous charge spark ignition 
• Stratified charge compression ignition

Controlling the HCCI is the major problem and it control must be effected by :

• Variable compression ratio
• Variable induction temperature
• Variable exhaust gas percentage
• Variable valve actuation
• Variable fuel ignition quality

Advantages of the HCCI engine :

• Fuel-saving 
• Lean fuel operated diesel-like compression ratio
• High efficiency than conventional SI engine
• Clean combustion and lower emissions
• The peak temperature is lower than the SI engine
• NOx and soot emissions are negligible
• Operated on all alternative fuels
• Low throttling losses

Disadvantages of HCCI engine :

• High in-cylinder pressure may cause damage to the engine
• Fast heat release and pressure rise contributes to engine wear
• Auto-ignition is difficult to control
• Constraints at low load
• Small power range
• Problems at high load condition because of cylinder pressure restrictions
• CO emissions are high as compared to SI engine 

Explore more information: 

1. Advantages and disadvantages of HCCI engine