Characterization, at Partial Loads, of the Combustion and Emissions of a Dual-Fuel Engine Burning Diesel and a Lean Gas Surrogate

For decentralized power generation in West Africa, gas from a small biomass gasification unit can be used as the main fuel in a dual-fuel engine with diesel as the pilot fuel. To study the combustion in this type of engine (Lister Petter), experiments were conducted with a surrogate gas composed of liquefied petroleum gas and nitrogen (LPGN2), the energy context of which is similar to that of syngas. The tests were conducted at different loads and for different diesel substitution rates. The combustion analysis showed that the LPGN2 mixture had an overall behaviour similar to neat diesel, while the pressure peaks were lower in dual-fuel mode. The results also indicated a longer ignition delay and a pronounced diffusive combustion phase leading to a lower indicated mean effective pressure with gas. The fuel efficiencies remained low in both mono- and dual-fuel operation. The relative instability of the combustion in dual-fuel mode gave rise to an increase in the coefficient of variation (COVIMEP). Compared to neat diesel, the engine running at low loads in dual-fuel mode showed higher emission levels of CO, a slight reduction of 2.5% of CO2 and a substantial decrease of 73% for nitrogen oxides.