Spark assisted premixed charge compression ignition engine prototype development

Abstract

Thermal efficiency of compression ignition (CI) engine is higher than spark ignition (SI) engine however heterogeneous fuel-air mixing in CI engine leads to higher NOx and soot formation. Fuel quality is deteriorating with time because of availability of heavier crude reserves. There is a need to use low volatility, low octane number fuels in the engines in an environment friendly manner. To investigate this, gasoline was blended with low volatility fuels such as diesel and kerosene. In order to improve fuel-air mixing, spark ignition of gasoline like fuels blended with low volatility diesel like fuels at higher compression ratio (11) was experimentally investigated in a prototype single cylinder partially premixed charged compression ignition (PCCI) engine. Experiments were conducted at a constant engine speed using five test fuels namely GD5 (5% v/v diesel blended with 95% v/v gasoline), GD15 (15% v/v diesel blended with 85% v/v gasoline), GK5 (5% v/v kerosene blended with 95% v/v gasoline), GK15 (15% v/v kerosene blended with 85% v/v gasoline) and G100 (100% gasoline), which was used as baseline fuel. Relative air-fuel ratio (RAFR) was maintained at 0.95 to avoid misfire at lower engine loads. Mixing and manifold injection of gasoline blended with diesel and kerosene was carried out at low pressure (3bar) using a customized common rail fuel injection system. Spark plug was used for triggering the start of combustion at a fixed spark timing of 25° bTDC. Compression ratio of spark assisted partially premixed charge compression ignition (SAPCCI) engine was kept lower than conventional CI engine to avoid auto-ignition of test fuels however it was higher than conventional SI engine to achieve greater thermal efficiency. Fuel injection timing and injection duration were controlled by a customized electronic circuit. Engine performance, emissions and combustion characteristics were investigated and compared with baseline gasoline at different engine loads. GK5 and GD5 blends exhibited higher brake thermal efficiency than baseline gasoline in SAPCCI mode, which suggested that low volatility fuels can be used in SAPCCI mode in an engine efficiently.