Investigation of Auto-Ignition of Heptane-CNG Mixture in HCCI Engine

Homogeneous Charge Compression Ignition (HCCI) operating principals have been widely investigated yet the uncontrollable combustion of HCCI is the major obstacle in its development. This paper is trying to increase the understanding on the auto-ignition and combustion process of several fuels to be applied in HCCI combustion system. This paper investigates variation of fuel composition between heptane and compressed natural gas (CNG) with the composition ranges from 10-100% heptane/CNG. The investigation was done in a constant volume chamber with elevated temperature (800°C). Three lambdas were tested for each fuel, namely 0.8, 1, 1.2 and 2. From the results, it is found that the mixture composition highly affects the output of the combustion of dual fuel where CNG is able to suppress heptane combustion at CNG percentage more than 40%. Furthermore, homogeneity level highly determines the types of combustion produced by the mixture, distributed or propagation flame.