Combustion Instability Analysis of Dual-Fuel Stationary Compression Ignition Engine Using Statistical Method and Wavelet Transform

This study examines the cycle-to-cycle variations (combustion instability) in the dual-fuel stationary compression ignition engine. The variations in the consecutive engine cycles are characterized under different load, gasoline/methanol-diesel premixing ratio (r_p) and diesel injection timing (SOI). To investigate the combustion instability in dual-fuel CI-engine, gasoline and methanol are used as a low reactivity fuel (LRF) and is fed in the modified intake manifold during the suction stroke. The tests are performed for different fuel r_p using developed port-fuel injector controller in the laboratory. The combustion instability is analyzed using the statistical method and Wavelet Transform (WT). Results indicate that combustion instability is more prone to lower and medium engine load, and variations are significantly higher for the high substitution fraction of LRF. The upper limit of fuel r_p is restricted by higher variations in the combustion parameters. WT analysis shows that the peak power in global wavelet spectrum (GWS) increases with an increase in the LRF substitution fraction, which indicates higher cyclic variations. When the engine operation is shifted from conventional diesel to dual-fuel mode, the peak power in GWS shifted from higher to lower periodicity, which depicts the frequency of cyclic combustion variations increases in dual-fuel combustion mode. The cyclic combustion variations in dual-fuel CI-engine is possibly due to the variations in the start of combustion, which are susceptible to variations in fuel flow characteristics in the stationary engine.