Effects of Air Excess Ratio on Combustion and Engine Performance in a Homogeneous Charge Compression Ignition Engine fuelled with Hexane and N-Heptane Fuel Mixtures

Abstract

Homogeneous charge compression ignition engines are engines with low temperature combustion tendency and high thermal efficiency. The operating range of these engines, where there is no direct control over combustion, is limited because of knock and misfire problems. At this point, it is aimed to eliminate the knocking problem especially at high loads with the mixture composition taken into the cylinder and different operating parameters. HCCI combustion is highly affected by engine operating parameters. In this study, a single-cylinder four-stroke spark-ignition engine was converted to a homogeneous charge compression ignition engine. The test engine was operated with hexane and n-heptane fuel mixtures at 1400 rpm and between 1.9 and 2.74 air excess ratio in full load HCCI combustion mode. The effects of hexane fuel on cylinder pressure, heat release rate, in-cylinder temperature, combustion duration, start of combustion, cyclic variations, knock density, indicated mean effective pressure (imep), thermal efficiency and emissions (HC and CO) were investigated experimentally. In the experiments carried out at constant intake air inlet temperature, it was observed that the cylinder pressure and heat release rate decreased with increasing air excess ratio. As a result, HCCI combustion was found to be highly affected by air excess ratio and fuel composition. It has also been found that the range of operation can be extended in the knock boundary zone in HCCI combustion.

Keywords

• air fuel ratio
• hexane
• homogeneous charge compression ignition
• engine performance