Part Load Characterization of a Small-Bore Diesel Piloted Dual Fuel Compression Ignition Engine with Methane
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A 0.8L, 3 cylinder turbocharged diesel engine was retrofitted for premixed and port injected dual fuel operation. Diesel baseline testing was conducted and conventional diesel trends in efficiency and emissions were found in relation to pilot start of injection (SOI) and load. However, at low loads the combustion mode deviated from a conventional diffusion flame. The end of injection was found to occur well before start of combustion (SOC), suggesting that combustion was closer to premixed charge compression ignition (PCCI). Dual fuel mode operation was carried out using two methods. First, the fuel proportions were varied while maintaining 25% full load (FL). The brake fuel conversion efficiency (BCFE), unburned hydrocarbons (UHC) and CO emissions suffered, while NOx emissions and peak pressure decreased with increased methane substitution. Ignition delay increased with methane substitution. Port injected dual fuel modes yielded improved BFCE, but similar UHC and CO emissions compared to premixed dual fuel. Second, constant pilot tests with small pilot quantities resulted in decreased BFCE and increased CO and UHC emissions compared to diesel-only. Increasing load resulted in improved BFCE relative to diesel performance and decreased UHC and CO emissions. Constant pilot NOx emissions were lower than diesel-only at low load, but far exceeded diesel levels above 50%FL. Increased pilot injection quantity provided emissions and BFCE benefits compared to the minimum pilot quantity for low loads only (below 50%). Advancing SOI increased peak cylinder pressure and temperature, and improved UHC and CO emissions. Further advancement resulted in decreased BFCE due to very early heat release (BTDC). Similarly at 50%FL SOI advance increased peak pressure and temperature. Much less improvement in BFCE was found with SOI advancement, but UHC and CO emissions were reduced. At very early SOI angles SOC and peak pressure was retarded and yielded a slow ignition event followed by a single heat release event. Increasing the load and/or pilot quantity resulted in further advancement of SOI timing compared to the smaller pilot quantity. All tests reported in this thesis were conducted at an 1800RPM nominal engine speed.