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The main aim of this study is to investigate the effect of NO and NO2 on the combustion characteristics such as pressure development and combustion phasing in natural gas HCCI engine. A secondary aim is to demonstrate a method of obtaining a significant sensitizing effect on methane oxidation reaction from small amounts of NOx. Experiments were conducted using a rapid compression-expansion machine that was constructed from a single-cylinder diesel engine. First, the sensitizing effect of NO and NO2 on the HCCI combustion of natural gas was investigated in a case where NOx was uniformly mixed into a charge. Obtained results show that the auto-ignition timing is significantly advanced and an acute heat release is promoted by adding either NO or NO2.

This study focuses on deposit formation in a diesel engine fueled with straight vegetable oil (SVO) and its effects on engine performance and exhaust emissions. First, two-dimensional thickness distributions of the carbon deposits on the cylinder head were measured by a laser displacement meter after continuous engine operation on gas oil blended with SVO at 25%. The obtained results show that the carbon deposit thickness rapidly increases with SVO-blended fuel and reaches a higher level than with just gas oil. Second, the effects of fuel injector deposits on engine performance and emissions were examined. A small diesel engine was continuously operated by alternating between SVO and gas oil. Gas oil was injected for 1 hour before and after 6 hours of SVO operation to prevent the accumulation of SVO deposits inside the nozzle holes, and the process was repeated.