Analysis of Fuel Properties on Combustion Characteristics in a Narrow-Throat Pre-Chamber Engine 2021-01-0474

In this study, the authors investigated the effect of fuel properties on the combustion characteristics by employing methane, methanol, ethanol, and primary reference fuels (PRFs) as the main chamber fuel while using methane for the pre-chamber. Global excess air ratios (λ) from 1.6 to lean limit were tested, while 13% of total fuel energy supplied to the engine was delivered via the pre-chamber. The gaseous methane was injected into the pre-chamber at the gas exchange top-dead-center (TDC). Port fuel injection was tested with both open and closed inlet valves. The pre-chamber assembly was designed to fit into the diesel injector pocket of the base engine, which resulted in a narrow throat diameter of 3.3 mm. The combustion stability limit was set at 5% of the coefficient of variation of gross IMEP, and the knock intensity limit was set at 10 bar. GT-Power software was used to estimate the composition of pre-chamber species and was used in heat release analysis of the two chambers. It was found that the rich limit was controlled by engine knock. Hence a higher reactivity fuel (lower octane) had to be operated leaner. However, with the increasing reactivity, the lean limit was also extended, while the peak efficiency was also obtained with a leaner mixture. With PRF 90, the lean limit was at global-λ = 3.0, while the limit was 2.3 with methane. The alcohol fuels exhibited a different behavior from the methane and the PRFs. Ethanol has the same lean limit as PRF100, but methanol could be operated up to global-λ = 3.2. The pre-chamber combustion did not change much with the different fuels in the main chamber, so the combustion stability trends must be related to the transition from burning jets to ignition of the main chamber charge and its subsequent combustion.