Effects of Open-Valve and Close-Valve Injections on the Performance of a Port Injection Methane Engine

Increasing concerns over energy security and stricter legislation on automotive exhaust emission limits have triggered greater efforts in utilizing alternatives to petroleum-based fuels. Compressed natural gas (CNG) is one of the promising candidates in terms of emissions and price. In this paper, methane, the major constituent of natural gas (NG), in used to fuel a Ricardo E6 engine and run in a port injection operation with open-valve and close-valve injection. The compression ratio is set at 10.5:1. Methane at 30 bar was supplied to the injector and injection length was adjusted to achieve the desired air fuel ratio (AFR). The minimum advance for best torque (MBT) was determined for 1100 rpm speed by measuring the indicated mean effective pressure (IMEP) for combustion at spark advance between 14°CA and 35°CA BTDC. The result is clearly demonstrated that the performance of the open valve port injection (OVPI) is superior to the one of the close valve port injection (CVPI) with better IMEP, fuel conversion efficiency, indicated power and volumetric efficiency. The observation indicates that OVPI shows steadiness of peak pressures shifts toward top dead centre (TDC) as spark ignitions were advanced compared to CVPI. In terms of combustion characteristics, the OVPI operation yields shorter ignition delay and overall burning duration even at the same phasing angle. Therefore, the open valve operation is preferable for NG port injection due to the fact that injections take place while intake valve is open. It accelerates the charge flow into the cylinder causing higher volumetric efficiency and avoiding the back pressure that happen when high pressure methane is injected while intake valve closes.