Effect of turbulence and multiple injection strategies on homogeneous charge compression ignition (HCCI) diesel engines ? a review

Combustion in HCCI engines occurs simultaneously throughout the volume of combustion chamber rather than in a flame front. This approximates constant volume combustion in HCCI engines resulting in higher thermal efficiency?and lower nitogen oxides (NOx) and particulate matter (PM) emissions. However, it employs higher compression ratio and lacks a threshold value resulting in shorter combustion duration and fast combustion rate leading to higher peak in-cylinder?pressures. This paper reviews the effect of turbulence and multiple injection approaches on HCCI diesel engines. Turbulence can be induced by increasing the swirl ratio (SW) which will reduce peak pressures inside the combustion chamber. However, increased SW increases carbon monoxide (CO) emissions. Two types of combustion chamber designs were mainly?used to induce turbulence, one with square type and the other disc type. Square bowl engine results in higher turbulence and causes higher combustion duration and slower pressure rise compared to the disc engine. NOx emissions in dual injection case were higher when compared to?the?single injection. It was found that by increasing the first injection pulse duration, fuel injected in the premixed combustion phase will become large when compared to the diffusion phase, leading to the reduction in heat release rate, thereby reducing NOx emissions significantly.