Determination of Efficiency Losses in Entry Ignition Engines 2021-01-0441
In 2020, Cheeseman (SAE Paper 2020-01-1314) introduced Entry Ignition (EI) as a potential engine combustion process to rival traditional Spark Ignition (SI) and Compression Ignition (CI). The EI process premixes fuel with compressed air, which then enters a hot cylinder at top dead center, autoigniting upon entry. The original proposed concept for an engine separates the compression and expansion processes allowing for it to be modeled as a 2-stroke Brayton cycle. Theoretically, an EI engine allows for higher compression ratios than SI engines with less emissions than CI engines. However, the original EI engine analysis made several assumptions that merit further investigation. First, the original analysis did not look at the temperatures and pressures in the air/fuel mixing chamber to ensure that it does not autoignite prior to entering the cylinder. Second, the analysis did not account for the large amount of heat transfer associated with keeping half the end-gas in the cylinder. Third, the analysis neglected the losses caused by intake passageways and additional components. Our analysis corrects Cheeseman’s thermodynamic model to account for these changes to better identify a brake thermal efficiency for the EI cycle. Our analyses further identify other issues with the EI process to include frictional losses, operating at partial load, and emissions. With these corrections, the EI engine was found to perform with a similar or less efficiency than SI engines. Additionally, while it has the potential to reduce NOx emissions, the large quantity of residuals can result in an increase in CO emissions.