A Study of Ignition Characteristics of an HCCI Engine Operating on a Two-component Fuel

The Homogenous Charge Compression Ignition (HCCI) engine is positioned as a next-generation internal combustion engine and has been the focus of extensive research in recent years to develop a practical system. One reason is that this new combustion system achieves lower fuel consumption and simultaneous reductions of nitrogen oxide (NOx) and particulate matter (PM) emissions, which are major issues of internal combustion engines today. However, the characteristics of HCCI combustion can prevent suitable engine operation owing to the rapid combustion process that occurs accompanied by a steep pressure rise when the amount of fuel injected is increased to obtain higher power output. A major issue of HCCI is to control this rapid combustion so that the quantity of fuel injected can be increased for greater power. Controlling the ignition timing is also an issue because it is substantially influenced by the chemical reactions of the fuel. Various approaches are being researched for expanding the range of stable engine operation, including the application of turbocharging, the use of residual combustion gas, stratification of the fuel concentration, and the use of a blend of two types of fuel having widely different ignition characteristics.

This study focused on the use of a mixture of two fuels with different ignition characteristics. Experiments were conducted using a blend of n-heptane (0 RON) as a readily autoignitable fuel and iso-octane (100 RON) as a fuel non-conducive to autoignition. The results showed that this approach enables the amount of fuel injected to be increased while controlling the ignition timing.