Injection of a H 2O 2/water solution into the combustion chamber of a direct injection diesel engine and its effect on soot removal

Abstract

Hydrogen peroxide (H2O2) dissolved in water was injected into the combustion chamber of a direct injection (DI) diesel engine at different crank angles. Its effect on the general combustion characteristics was followed by crank angle (CA) resolved pressure and OH radiation measurements inside the combustion chamber. The influence on soot mass in the exhaust gas flow was measured by the Bosch Smoke Number, which is the stadard measurement technique in internal combustion engine research. Additionally, the concentrations of unburned hydrocarbons (HC) and nitric oxides (NOx) were recorded by a gas analyzer. For both, the spray of H2O2/water and pure water, a clear decrease in soot emission was observed for early injection at crank angles −40°<CA<−10o before top dead center (BTDC), which is associated with an increase in the exhaust gas HC concentration. For these conditions, the soot removal is mainly an effect of compressed air coolig, which increases the induction time of the diesel spray, thus resulting in a shift toward more premixed combustion. At injection crank angles CA>+10o, the water and the H2O2/water sprays show an opposite behavior with respect to the exhaust gas soot. The in-cylinder measurements clearly show an increase of OH radiation during cycles with H2O2/water injection compared to the standard engine conditions. The H2O2 decomposition product OH influencs the chemistry of the in-cylinder soot oxidation, which results in a decrease of the soot mass in the engine exhaust gas flow. Concentrations of HC and NOx are not significantly affected. The addition of pure water causes an increase in the exhaust gas soot for spray injection crank angles CA <+10o.