Modelling of high efficiency multi-fuel two-stroke gas engine systems

[摘要] In order to study the knock threshold gaseous fuels, a rapid compression machine (RCM) has been used. As natural gas contains mostly methane as well as small proportions of various hydrocarbons with different weights, this work focuses on obtaining the influences of blending separately various proportions of ethane, propane, butane and finally n-pentane into methane. These fuels were selected to investigate the effects of the high and low methane number (MN) mixtures on the combustion phenomenon of real reciprocating engines. The idea behind this machine is to better understand different phenomena associated with the operation of internal combustion engines. The evolution of the RCMs and the development of new machines capable of increased control over experimental conditions are essential to the refinement of combustion modelling processes. An experimental study into the variation of the peak pressure and compression ratio was conducted on the aforementioned mixtures. As the mixture contains a higher proportion of methane, higher driving pressure is required to achieve the knock threshold operating condition. The peak pressure and compression ratio reduce as the methane content in the mixture reduces by blending heavier hydrocarbons; however, the rate of reduction slows down for methane-ethane, methane-propane and methane-butane mixtures. As pentane is mixed into the methane, the peak pressure and compression ratio decline rapidly and never slow down. A further investigation into the ignition delay, EOC pressure and temperature has been conducted. The ignition delay of the mixtures varies between 0.6 ms and 0.9 ms at knock threshold operating points, with lambda 1.2; except the ignition delay time of methane-pentane mixture which soars rapidly from 1.1 ms to 2 ms. The EOC pressure and temperature decline gradually for the lower proportions of the methane content in the mixture; however, there is a huge drop in the mixture of 8% pentane with 92% methane. Later in the work, the methane number of the mixtures based on the peak pressure and compression ratio have been presented. It identifies that the MN and either Pmax or CR are proportional together, except when the methane is blended with high proportions of ethane in the mixture. A high content of ethane leads to drop the mixture resistance, since the MN calculator is not able to calculate it accurately. A 1-D engine simulation model has been created in the AVL BOOST to calculate the heat release rate and mass fraction burnt. Special attention has been given to valve timing and piston motion definitions to simulate the RCM in the BOOST platform, as it is not a complete reciprocating engine and the piston stays at its position during the intake and exhaust processes.

[发布机构] University:University of Birmingham;Department:School of Mechanical Engineering

[关键词] T Technology;TJ Mechanical engineering and machinery