Enhancement of Combustion of Vegetable Oil in Diesel Engines at Low Loads with Hydrogen

One of the fundamental problems associated with combustion of vegetable oils in diesel engines is their poor combustion at low engine speeds and loads. As a possible remedy to this problem, co-firing of small amount of gaseous hydrogen introduced into the intake air was investigated on a mechanically controlled direct injection turbodiesel tractor engine. The engine was operated at idle and several low-rpm, low-load points on fuel-grade rapeseed oil heated to 60–70°C, with up to 5.5% of hydrogen by volume (600 g/h) injected into the intake air. Emissions of HC, CO, and NO_x have all markedly decreased with increasing hydrogen concentrations. At higher hydrogen concentrations the onset of the combustion became noticeably delayed and the peak combustion pressure has decreased. The results suggest that the addition of a relatively small amount of hydrogen into the intake air of an engine running on heated rapeseed oil at low rpm and low load can bring the emissions of HC and PM, normally several times higher compared to operation on diesel fuel, back to their “diesel” level. This might also aid in preventing the buildup of deposits within the engine under such operating conditions. It is expected that the effect of the hydrogen co-firing can be further enhanced by optimization of the injection timing and other parameters.