Frank Atzler

The effect of closely coupled pilot injections on diesel engine emissions

Modern common rail fuel injection systems allow for very sophisticated injection strategies to facilitate the compromise between low emissions, fuel consumption and combustion noise. One such injection strategy is the reduction of the dwell time between injections to extremely low values.

Multiple small vs single large pilot injections for Diesel engines

ABSTRACT Diesel engines have to fulfil a number of conflicting requirements. Apart from the ever tightening emissions legislations throughout the world there is also a strong move towards reducing the fuel consumption. Additionally the issues of noise, vibration and harshness have to be satisfied, in particular for passenger car engines. The trade offs of particulate matter against nitrous oxides and against combustion noise can to some extent be overcome by injection rate shaping. In previous publications the authors presented the effects of various injection strategies throughout the engine map. The current work will try to elucidate the functioning of some of these strategies, including very short dwell times between injections, the so-called “Minimum Dwell”. MinDwell was realized by means of the Continental direct drive piezo injector, and was found to be effective throughout the engine map. At low load it helped to reduce the emissions of hydro carbons and carbon monoxide, at higher part load and full load it reduced PM and combustion noise. 3D CFD simulation was employed as a “virtual transparent engine” to investigate the physical processes for a successful application.