Diesel Engine Acoustic Emission Analysis for Combustion Control 2012-01-1338

Future regulations on pollutant emissions will impose a drastic cut on Diesel engines out-emissions. For this reason, the development of closed-loop combustion control algorithms has become a key factor in modern Diesel engine management systems. Diesel engines out-emissions can be reduced through a highly premixed combustion portion in low and medium load operating conditions. Since low-temperature premixed combustions are very sensitive to in-cylinder thermal conditions, the first aspect to be considered in newly developed Diesel engine control strategies is the control of the center of combustion. In order to achieve the target center of combustion, conventional combustion control algorithms correct the measured value varying main injection timing.

A further reduction in engine-out emissions can be obtained applying an appropriate injection strategy. Modern Diesel engine injection systems allow designing injection patterns with many degrees of freedom, due to the large number of tuneable injection parameters (such as start and duration of each injection). Each variation of the injection parameters will affect and alter the whole combustion process and, consequently, pollutant emissions production. Furthermore, injection parameters variations have a strong influence on other quantities that are related to combustion process effectiveness, such as noise radiated by the engine.

This work discusses the correlations existing between in cylinder pressure and the acoustic emission radiated by the engine. In order to set up the correlations that allow noise prediction starting from in-cylinder pressure measurement, several experimental tests have been performed, both in steady state and transient conditions, on a Diesel engine mounted in a test cell. Each operating condition was run both activating and deactivating pre-injections. As it is well known, in several low load conditions, pre-injections deactivation produces a decrease in pollutant emissions production (especially in particulate matter) and a simultaneous increase in engine noise. The investigation of the correlation between combustion process and engine noise can be used to set up a closed-loop algorithm for optimal combustion control based on engine noise prediction.