Analysis of the Potential of Biodiesel as an Alternative Fuel for Current and Future HSDI Engines 2009-01-0480
In this paper the effect of the engine load and the EGR (exhaust gas recirculation) rate on the combustion process and the pollutant emissions when using RME (rapeseed methyl-ester) is investigated. For this purpose a parametric study in a single-cylinder HSDI (high speed direct injection) engine in a wide range of operating conditions (thus trying to maximize the generality of the results) has been carried out.
All the output parameters are compared with the corresponding ones for a reference diesel fuel at equivalent engine performances and operating conditions. To perform a rigorous comparison, a specific methodology has been designed based on the comparison at equivalent engine load and oxygen mass fraction in the intake manifold, so as to remove the effect of the fuel properties (derived from the different oxygen content, mainly) on the engine performances.
The results show that the important reduction in soot, CO and UHC emissions and the small increase in NOx emissions when RME is used instead of standard diesel fuel, traditionally observed in typical engine operating conditions, still applies to high dilution (i.e., low in-cylinder oxygen mass fraction) conditions necessary for EURO-6. As already known, the slight increase in NOx can be largely compensated with a higher EGR rate without a noticeable penalty in the rest of pollutants.
The use of biofuels seems a very promising path to reduce pollutant emissions in a diesel engine while preserving its high efficiency, because it avoids problems with engine control and transition between different operating modes associated to HCCI (homogeneous charge compression ignition) engines, for instance.