Abstract
The HCCI (Homogeneous Charge Compression Ignition) engine is an internal combustion engine under development, which is capable of providing both high diesel-like efficiency and very low NOx and particulate emissions. However, several technical issues must be resolved before the HCCI engine is ready for widespread application. One issue is that its operating range is limited by an excessive pressure rise rate which is caused by the excessive heat release from its selfaccelerated combustion reaction and the resulting engine knock in high-load conditions. The purpose of this study was to evaluate the potential of thermal and fuel stratification for reducing the pressure rise rate in HCCI engines. The NOx and CO concentrations in the exhaust gas were also evaluated to confirm combustion completeness and NOx emissions. The computational work was conducted using a multi-zone code with detailed chemical kinetics, including the effects of thermal and fuel stratification on the onset of ignition and the rate of combustion. The engine was fueled with dimethyl ether (DME) which has a unique two-stage heat release, and methane which has a one-stage heat release.
Highlights
In HCCI, a premixed air/fuel mixture is inhaled to the combustion chamber and ignited by adiabatic compression
Based on result of 2-zone model, reducing gas pressure rate, heat release and emission is investigated in combustion chamber when there is more temperature and fuel distribution by using the numerical analysis at 5 model-zone to expand and vary the stratification
Using the DME and Methane, the relation between CA50% and maximum pressure rise rate is shown in Fig..[13-16] in condition of average equivalent ratio(φ=0,25) and changing the average temperature before the compression from T0=300K to T0=500K
Summary
In HCCI, a premixed air/fuel mixture is inhaled to the combustion chamber and ignited by adiabatic compression. The HCCI engine, which is using the bulk combustion, is promising concept of the high efficient and low emission engine. Power produced in HCCI engine is limited by knocking cause of excessive heat release and pressure rise at local area in condition of high load. The main investigation of the HCCI is avoiding knocking problem to be able to operate at a high load. Delaying the combustion angle and stratifying temperature or concentration of fuel resulting in dispersion of combustion timing is the well-known effective method. Effect of the pressure increase rate in combustion chamber by stratified temperature and fuel concentration of pre mixture according to fuel characteristic was investigated. Numerical analysis in chemical reaction was conducted for investigating an emission property
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