Investigation of High Pressure/Late Cycle Injection of CNG (Compressed Natural Gas) as a Fuel for Rail Applications

摘要

This report describes a demonstration effort to investigate the use of natural gas in a medium-speed diesel engine. The effort was unique in the sense that natural gas was injected directly into the combustion chamber late in the compression stroke, as a high pressure gas rather than through low pressure fumigation or low pressure injection early in the compression stroke. Tests were performed on a laboratory two-cylinder, two-stroke cycle medium-speed diesel engine in an attempt to define its ability to operate on the high pressure/late cycle injection concept and to define the performance and emission characteristics of the engine under such operation. A small quantity of No.-2 diesel fuel was injected into the cylinder slightly before the gas injection to be used as an ignition source for the gas. Pilot (diesel fuel) and main (natural gas) timing and injection duration were systematically varied to optimize engine performance. The test demonstrated that the medium-speed engine was capable of attaining full rated speed and load (unlike the low pressure approach) with very low percentages of pilot injection with the absence of knock. Thermal efficiency was as much as 10 percent less than thermal efficiency levels obtained with neat diesel fuel. This was primarily due to the placement and injection characteristics of the pilot and main injectors. Optimization of the injection system would undoubtedly result in increased thermal efficiency. 11 figs., 4 tabs. (ERA citation 13:034232)