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For large bore Otto gas engines a high specific power output and therefore high engine load promises a rise in engine efficiency on one hand and on the other hand a reduction of the performance-related investment. However, this can negatively affect the emissions performance, operating limits especially in regards to knocking, and component life. For this reason at the Chair of Internal Combustion Engines (LVK) of the Technical University of Munich (TUM) experiments with a 4.77 l single-cylinder research engine were carried out to investigate the boundary conditions, potentials and downsides of combustion processes with a brake mean effective pressure beyond current series engines and higher than 30 bar. The objective in this investigations was to achieve BMEP > 30 bar with an engine configuration that widely represents the current series-production status. Hence, an unscavenged prechamber spark plug, a series Piston and Valve timing were used.

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.