Effect of natural gas conditions on combustion characteristics and overall performance of a novel bimodal internal combustion engine
نویسندگان
چکیده
Abundant availability and potential for lower CO2 emissions are drivers for increased utilization of natural gas in automotive engines for transportation applications. However scarce refueling resources for on-road vehicles impose an infrastructure limited barrier on natural gas use in transportation. A novel ‘bimodal’ engine which can operate in a compressor mode has been developed that allows on-board refueling of natural gas where available without the need for any supplemental device. Engine compression of natural gas however results in altering the initial state of the fuel with potential impact on combustion characteristics and overall engine performance. Increase in natural gas temperature and addition of oil are two key effects attributed to the onboard refueling process. A secondary effect is the presence of water in the natural gas supply line. This study aims to investigate these effects by coupling an upfront system model of the onboard refueling process with a thermodynamic model of the engine processes. Parametric studies will be undertaken to study the effects of variation in natural gas inlet temperature, oil and water content on ignition, flame propagation and auto-ignition processes. Inlet fuel temperature has a strong influence on unburned hydrocarbons released in the exhaust while presence of heavier hydrocarbons due to the oil content can influence auto-ignition characteristics. Another effect of implementing the onboard refueling setup is that it requires altering the spark plug placement in the cylinder head. The influence of this modification will be additionally studied through literature review. Overall, this work attempts to model the influence of the upstream natural gas refueling stage on downstream combustion processes to verify that engine metrics such as overall efficiency, coefficient of variation, and hydrocarbon emissions are maintained at an acceptable level to ensure clean combustion.
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