Analysis of a Prechamber Ignited HPDI Gas Combustion Concept 2020-01-0824
Direct gas injection of natural gas under high pressure (HPDI) into the combustion chamber enables a non-premixed combustion regime known from diesel engines. With this combustion process, knocking combustion cannot occur, enabling an increase in the compression ratio and thus, a possible increase in efficiency. Due to the high injection pressures required, this concept is ideally suited for applications where liquefied natural gas (LNG) is available. In marine applications, the bunkering of and operation with LNG is state of the art.
Existing HPDI gas combustion concepts typically use a small amount of diesel fuel for ignition, which is injected late in the compression stroke. The diesel fuel ignites due to the high temperature of the cylinder charge. The subsequently injected gas ignites at the diesel flame. The presented HPDI gas combustion concept is of a monovalent type, meaning that no other fuel than natural gas is used. The high-pressure gas jet is ignited with the aid of flame torches from a gas-scavenged prechamber.
Design and layout of the combustion process and the prechamber shape was simulation-based. Predesign and validation on the single-cylinder research engine (SCE) were presented in SAE Technical Paper 2019-01-0259. More detailed results of the measurements at the SCE are presented and discussed in this paper. The results clearly demonstrate the high number of degrees of freedom of the prechamber ignited HPDI gas combustion concept. The publication shows investigations on the influence of injection timing, ignition timing in the prechamber and gas supply pressure. Potential measures for improvement will be outlined. Finally, a concept comparison between the prechamber ignited HPDI gas combustion concept and a representative diesel combustion concept is made. This shows that the expected properties have been met and illustrates the advantages and disadvantages of the new combustion concept.
Jan Zelenka, Gernot Kammel, Andreas Wimmer, Enrico Bärow, Matthias Huschenbett
LEC GmbH, Graz University of Technology, Woodward L'Orange GmbH, Hoerbiger Wien GmbH