Comparisons of the Cyclic Variability of Gasoline/Diesel and Ethanol/Diesel Dual-Fuel Combustion Based on a Diesel Engine 2017-01-5001
In this paper, experiments and simulations were conducted to investigate the cyclic variations of gasoline/diesel and ethanol/diesel dual-fuel combustion. For both dual-fuel modes, gasoline and ethanol were injected into the intake port during the intake stroke and diesel was directly injected into the cylinder. The influences of engine load and port fuel proportion on the cyclic variability of both dual-fuel modes were investigated. At each test condition, in-cylinder pressure traces of 150 consecutive cycles were acquired. Then the cyclic variations of ignition timing (CA5), combustion phasing (CA50), accumulated heat release (Qf) and indicated mean effective pressure (IMEP) were calculated based on the in-cylinder pressure. The experimental results showed that the cyclic variation of IMEP was mainly caused by the variation of Qf for both dual-fuel modes. It was also found that the gasoline/diesel dual-fuel mode could achieve comparable variations with diesel engines at the higher load. However, the ethanol/diesel dual-fuel mode exhibited larger cyclic variations than the gasoline/diesel at the same test conditions. The cyclic variations of the ethanol/diesel dual-fuel mode increased gradually with the increasing ethanol proportion at both loads. The simulated results showed that the combustion of premixed ethanol exhibited larger variations to initial in-cylinder temperature fluctuations than gasoline at the light load. This was mainly due to the reduced combustion temperature and lower reactivity of ethanol. And the fluctuations in the combustion of premixed fuel contributed to higher cyclic variations.