Methods of Improving Combustion Efficiency in a High-Efficiency, Lean Burn Dual-Fuel Heavy-Duty Engine

Combustion losses are one of the largest areas on inefficiency in natural gas/diesel dual-fuel engines, especially when compared to the traditional diesel engines on which they are based. These losses can vary from 1-2% at high load, to more than 6% of the total fuel energy at part load conditions. For diesel/natural gas dual-fuel engines, the three main sources of combustion losses are: bulk losses (increasing air-fuel ratio, AFR, to the premixed fuel’s lean flammability limit), crevice losses (premixed fuel trapped near valve pockets and top ring lands unable to oxidize), and blow-through losses (fumigated fuel/air intake charge passes through the cylinder and out the exhaust valve during valve overlap). In order to improve overall engine efficiency and decrease greenhouse gas emissions, these losses must be minimized. In this paper, various mitigation techniques are explored experimentally on a 13 L, 2010-class on-highway diesel engine that has been modified for fumigated natural gas dual-fuel research. An additional study separated the effects of bulk and crevice losses on lean mixtures by adding H₂ to the fumigated natural gas to lower the mixture lean flammability limit, demonstrating that crevice losses are the dominant loss mechanism. Crevice-related combustion losses were then reduced by employing pistons with a decreased top ring-land height.