Book Description

The high-pressure direct-injection (HPDI) of natural gas in a compression ignition engine has the potential to reduce demand for petroleum derived fuels and significantly reduce the level of pollutants and greenhouse gases emitted from heavy duty transport vehicles. A new HPDI injector was tested where diesel is injected into a gas/diesel reservoir in the injector and the diesel and gas are then co-injected into the combustion chamber. In order to identify interactions between the diesel and gas in the reservoir, two different injector geometries were tested: prototypes A and B. Prototype B had reduced reservoir volume to increase gas velocity inside the injector. A majority of the tests were conducted in a single-cylinder test engine derived from a Cummins ISX diesel engine. As prototype A was being modified to create Prototype B this test engine was moved to a larger test cell. After updating the electrical, mechanical, and safety systems, the test engine in the new test cell was found to run repeatably; however, emissions comparisons between both test cells was not possible due to different analyzers being used. Single gas and double gas injections were conducted for both injector prototypes. The single gas injection tests found that increasing the diesel injection mass reduced the mass of gas injected. Increased diesel injection mass also shortened ignition delay, reduced unburned and partially burned fuel and increased NOx emissions. Holding the diesel injection mass constant and reducing the gas injection mass had the same effect as increasing diesel on ignition delay and gaseous emissions. If the diesel injection mass was kept constant and a second gas injection was added, the heat release due to the first injection decreased and the start of combustion was retarded. This appears to have occurred because some of the diesel was carried into the cylinder by the second injection and less diesel was available in the first injection to promote ignition. Double gas.