Impact of Gas To Liquid and diesel fuels on the engine cold start

- Gas To Liquid and diesel fuels were tested under cold engine start conditions.
- A methodology to evaluate different parameters from thermodynamic diagnosis has been developed.
- Parameters derived from on-line thermodynamic diagnosis have been studied.
- Clear effect of the engine coolant temperature on the rate of apparent heat release has been observed.
- The effect of cetane number is notable at low cold start temperatures.

Low ambient temperatures during start process have a notable influence on the combustion process. A methodology to study parameters as indicated mean pressure and rate of heat release, obtained using on-line thermodynamic diagnosis under cold start, was developed in this work. For this study, the correction of the pressure level from the first cycle measured has been made. Two ambient temperatures (20 °C and −7 °C) and two engine temperatures (20 °C and 70 °C) were selected for this study. A Gas To Liquid fuel and two diesel fuels (one of them with 5.8% of biodiesel) were tested in a Euro 4 diesel light-duty vehicle. Values of indicated mean pressure were higher during the first thermodynamic cycle than those corresponding to idle conditions with all fuels tested. Low engine temperature (20 °C) makes the combustion of fuel during pre-injection difficult and, consequently, only one peak of apparent heat release was registered. Fuel pre-injected burns together with fuel injected during the main injection. Besides, the effect of high cetane number of GTL is evident at low ambient temperature because its combustion takes place some degrees before compared to both diesel fuels tested.