Investigation of the High-Pressure-Dual-Fuel (HPDF) combustion process of natural gas on a fully optically accessible research engine

In the "high-pressure-dual-fuel" (HPDF) combustion process, natural gas is directly injected into the combustion chamber with high pressure at the end of the compression stroke, and burned in a diffusion flame similar to conventional diesel combustion. As natural gas does not self-ignite when injected into hot air, a small amount of diesel fuel is injected directly before the gas injection to provide an ignition source for the gas jets. The HPDF combustion process has the potential to substantially reduce methane slip compared to today's state of the art premixed lean burn gas engines, and furthermore, phenomena like knocking or misfire can be avoided completely. In this paper, the influences of in-cylinder air density and swirl motion on HPDF combustion is studied via high-speed recordings in a fully optically accessible 4.8 Liter single-cylinder research engine.