Revealing Fuel Effects On Catalyst Heating Operation Performance In An Optical Diesel Engine

Effective operation of diesel oxidation catalysts and selective catalytic reduction systems requires them to reach their light-off temperatures as quickly as possible after engine startup. Late–cycle heat release achieved using different post injection strategies has been identified as an effective approach to increase exhaust temperatures. Previous research has identified a tradeoff between exhaust temperatures and hydrocarbon (HC) emissions that limits post-injection retardability, and therefore the maximum achievable exhaust enthalpy. This work explores the effect of fuel properties, including cetane number, distillation characteristics, and oxygen content, on the tradeoffs, through experimental investigations on a single cylinder optical diesel engine. Increasing the cetane number 7 units (from 43 to 50) reduces HC emissions nearly by 60% with no significant changes in exhaust heat flux, whereas the HC emissions and exhaust heat flux for fuels with different distillation characteristics show lower sensitivity to post injection timings. Simultaneous high-speed visible and infrared imaging techniques are applied to analyze the effects of oxygenated blends on in-cylinder HC formation. Images show that the amount of unburned hydrocarbons formed by the post injections decreases as the oxygen content and the cetane number of the fuel increases likely because the mixing rate required to burn the fuel efficiently decreases with the oxygen content of the fuel, improving post-injection retardability. The addition of di-butyl ether improves the reactivity of the mixture, which promotes the faster penetration of main combustion in the squish region, which is also beneficial for HC reduction.