Search Results

Among the existing concepts that help to improve the efficiency of spark-ignition engines at part load, Controlled Auto-Ignition™ (CAI™) is an effective way to lower both fuel consumption and pollutant emissions. This combustion concept is based on the auto-ignition of an air-fuel-mixture highly diluted with hot burnt gases to achieve high indicated efficiency and low pollutant emissions through low temperature combustion. To minimize the costs of conversion of a standard spark-ignition engine into a CAI engine, the present study is restricted to a Port Fuel Injection engine with a cam-profile switching system and a cam phaser on both intake and exhaust sides. In a 4-stroke engine, a large amount of burnt gases can be trapped in the cylinder via early closure of the exhaust valves. This so-called Negative Valve Overlap (NVO) strategy has a key parameter to control the amount of trapped burnt gases and consequently the combustion: the exhaust valve-lift profile.

It is well known that high ethanol content fuels have to face poor quality regarding startability in cold conditions on a spark ignited engine. This paper will show test results when using E0, E85 and E100 fuels led on a single cylinder engine equipped with an active valve train research system. In order to improve engine behavior in severe thermal conditions, influence of several parameters was investigated. Injection strategies (timing, split injection, flow rate), valve train laws (delayed intake opening, valve lift…), ignition parameters (timing, multi-spark, strong energy coil…) as well as intake pressure were analyzed thanks to cylinder pressure analysis and specific test procedure. CFD investigations (influence of fuel, wall wetting) helped us to confirm some hypothesis on physical phenomenon. Those simulations were correlated with spray and wall film visualizations in the inlet port on an optical engine.