The Use of HCCI Combustion in a CFR Engine to Understand Fuel Behavior
The CFR engine is the standard to extract fuel autoignition tendency. The ASTM standard gives two numbers, Research Octane Number, RON, and Motor Octane Number, MON. The RON was defined 1928 and the MON slightly later. In both cases two reference fuels are used, Iso-octane (100) and n-heptane (0) and the engine compression ratio is increased until a certain level of knock is registered with a special microphone. The problem with this set-up is that the pressure and temperature path for the end gas will vary with the more or less stochastic SI flame propagation. An alternative way to rate fuel is replace the SI combustion with additional piston compression and switch to HCCI combustion. We can thus introduce a HCCI number equivalent of RON by running the engine at the same conditions (600rpm and 52°C inlet temperature).