Fuel Quality

For petroleum fuels many of the properties such as hydrocarbon composition, natural cetane number, volatility, viscosity and density are interdependent. As the fuel density decreases the fuel contains more of paraffinic hydrocarbons, which results generally in higher cetane number and fuel volatility and lower viscosity. So, the effect of change in one fuel quality parameter on emissions may be some times the result of several interactions. A high fuel cetane number improves cold starting and results in faster warm-up thus reducing cold engine HC emissions. As an increase in the cetane number reduces ignition delay it results in lowering of HC and NO _x emissions. On the other hand, with higher fuel volatility a larger lean flame out ‘overmixing' region may result and due to faster fuel evaporation the fraction of fuel burned during premixed combustion is also higher. Therefore, an increase in NO _x as well as HC may be observed with more volatile diesel fuels. The fuel sulphur increases sulphates in PM emissions increasing the particulate mass

Summary

The effect of various design and operating variables on DI diesel engine performance and emissions are summarized in Table 3.3.

Parameter	BSFC	BSNOx	BSHC	PM
Engine design variables
Compression ratio
Stroke/Bore ratio
Crevice volume
Swirl
Valve number
Fuel injection variables
Injection pressure
Retarded injection timing
Sac volume
Number of holes (size smaller)
Pilot injection
Eccentricity of Injector
Operating parameters
Engine speed
Engine load
Coolant temperature
Fuel cetane number
Fuel sulphur content
Fuel volatility