ESC-analys och studering av knack på en "Diesel Dual Fuel"-motor

Sammanfattning: A one-cylinder research engine has been used for studies with a Diesel Dual Fuel concept (DDF). DDF is a concept that utilizes a pilot diesel injection to ignite a homogenous natural gas/air mixture. Emissions and engine efficiency have been analyzed in an emission cycle called European Stationary Cycle (ESC) and the knock/pre-ignition problems with this type of engine have been investigated. At low and mid torque levels, an early diesel injection around 60 crank angles degrees (CAD) before top dead center (TDC) was used. At these loads raw NO xemissions was below EURO 6 level (0.2 g/kWh). NOxwas at EURO 5 level over the complete ESC without after treatment and with SCR at high loads it should be possible to reach EURO 6. One issue with DDF is the high HC emission levels. HC was approximately 40 g/kWh without after-treatment and by using an oxidation catalyst it should be lowered to around 10 g/kWh (approximated based on exhaust temperatures). Engine efficiency based on fuel flows and brake torque was within 26 - 40 % at different engine speeds and torque levels, which was lower than the same engine running with only diesel. The lower efficiency can be explained with the high amount of unburned hydrocarbons. Knock and pre-ignition was a problem at high loads and at medium loads when early diesel injection was used. The knock problems with this concept were highly dependent on the intake air temperature. Methods to avoid knock were tested. One way was to move the diesel injection a couple of CAD later. This was only applicable during the first knock cycles since several knock cycles in a row heated up the combustion chamber too much. Adding (more) EGR was also a good method to avoid knock.