Fuel suitability for low temperature combustion in compression ignition engines

The high load operations under low temperature combustion (LTC) strategies are investigated by using diesel, gasoline, n-butanol and ethanol, on the high compression ratio engines. In order to best suit the LTC operations, the fuel delivery strategies are designed in commensurate with fuel properties, for either a single fuel or the dual fuel uses. Engine tests are conducted at load levels of 0.8-1.2 MPa of indicated mean effective pressure (IMEP) to study the impact of fuel dispatching ratios, exhaust gas recirculation rates, and intake boost levels, along with the modulation of the diesel injection events. As the baseline tests the single shot diesel injection is firstly investigated under different levels of the boost and injection pressure. The knowledge of the auto-ignition characteristics of the port fuelling is studied with gasoline and applied accordingly to other fuels. The test results indicate that a volatile fuel, when delivered at an intake port, provides an advantage to enable LTC, i.e. suitable to produce a higher homogeneity for the cylinder charge. However, under a high compression ratio, a great deal of efforts is required for a port-dispersed fuel, such as gasoline or n-butanol, to withhold from the premature auto-ignition. The uncontrolled combustion events typically limit the engine load and worsen the soot and nitrogen oxides (NOx) emissions; whereas a lesser reactive fuel i.e. ethanol is preferred for the combustion control at high engine loads. The use of neat ethanol as a main energy supply along with the diesel fuel demonstrates superior performance of efficient combustion; whereupon under an optimized control, ultralow NOx and soot emissions are achieved for an engine load up to 1.7 MPa IMEP. When applied with a high-pressure direct injection strategy, an uncommonly tested fuel n-butanol is found more suitable to enable LTC than the diesel fuel. (C) 2013 Elsevier Ltd. All rights reserved.