Abstract
Due to the low volatility and high reactivity of conventional diesel fuels, the efficient combustion of a highly homogenous cylinder charge is normally limited to low loads. When the compression ratio, and thus the expansion ratio for prevalent engine designs, is substantially lowered to accommodate higher loads, the energy efficiency of the cycle is significantly reduced. In this work, with a high compression ratio of 18.2:1 kept intact on a single cylinder engine platform, the charge homogeneity is raised by adding fuels of higher volatility and lower reactivity at the intake port of the engine. The impact of port delivered gasoline has been reported by the authors previously; herein the usage of ethanol and butanol are investigated for their respective impacts on the enabling of ultra-low NOx and soot combustion at an elevated load level of 0.8 MPa IMEP. In order to attain appropriate combustion phasing with adequate burning completeness, the ratio of the port injection fuel and the direct (high pressure) injection fuel were adjusted; along with the modulation of the timing and events of the diesel pilot. The use of ethanol as a main fuel of energy supply demonstrated superior performance of clean and efficiency combustion for a load up to 1.36 MPa IMEP. Higher load operations have led to the premature auto-ignition of butanol and ethanol respectively, whilst butanol imposes the load barrier earlier than ethanol. Similar to the symptoms of most homogeneous charge engines, higher levels of total hydrocarbons and carbon monoxide emissions loom especially when excessive EGR is applied to defer the early heat-release. All the demonstrated tests are performed under the EGR and boost amounts that are considered readily achievable in an advanced production engine.
