Development and analysis of a split-cycle engine fuelled with methane.

摘要

Natural gas, which is primarily composed of methane, offers many advantages over other hydrocarbon fuels for use in reciprocating piston engines. Generally, these include: a high octane rating, wide flammability limits, a high gravimetric energy content, reduced CO2 output, and lower levels of harmful exhaust gas emissions. However, natural gas presents some unique challenges due to its low density and slow laminar burning velocity. The former causes issues with volumetric efficiency and/or charge homogeneity depending on the fuel delivery method. The latter results in prolonged combustion durations that are counter-productive to high fuel conversion efficiencies.;A split-cycle engine divides the conventional four-stroke engine process between two adjoining cylinders: one cylinder for intake and compression, the second cylinder for combustion and exhaust. The passage that connects these two cylinders together provides an alternative location for fuel injection and mixing. Furthermore, the fluid exchange process occurring from this passage to the combustion chamber is a source of turbulence generation desired to enhance the rate of combustion.;In this work a spark ignition split-cycle research engine has been developed and tested for the purpose of evaluating its ability to alleviate the aforementioned problems associated with natural gas (methane) fuelled engines. A novel fuel injector location and timing have been employed and the results show excellent mixture homogeneity was achieved. The fuelling strategy also decoupled the injection event from the engine's intake air flow rate; however, the volumetric efficiency still remained low, between 71-75%, due to flow losses in the compression cylinder. Combustion rates were found to be very rapid with both early and main burn duration periods on the order of 10-15°CA (crank angle), despite unfavourable burning conditions (i.e. low cylinder temperature and late combustion phasing). The exhaust gas emission levels of nitrogen oxide, carbon monoxide, and total unburned hydrocarbons were all below average values listed for spark ignition engines.