FUEL-COMPOSITION AND -VAPORIZATION EFFECTS ON COMBUSTION-CHAMBER DEPOSITS

It is known that gasoline extracted from coal and shale oil sources has higher end point fraction and higher aromatic content (hereafter known as HEPHAG) than typical normal end point gasoline (NEPG). Further, it is known that these HEPHAG can cause objectionable combustion chamber deposits (CCD). It was of practical interest (and the purpose of this thesis) to investigate whether HEPHAG would give acceptable combustion chamber deposits (i.e. comparable to NEPG) if introduced into a S.I. engine in a vaporized and homogeneous (gas phase) form. An analysis of the single cylinder results showed that regardless of the fuel, CCD decreased significantly when the fuel-air charge conditions were judged to be primarily gas phase. However, HEPHAG required a higher fuel-air charge temperature (FACT) than NEPG to realize this gas phase condition. An analysis of the multicylinder results showed that the vortex helped approach an equilibrium condition. Also, under conditions of high FACT and using the vortex, there was little difference in CCD formation between HEPHAG and NEPG tests. However, it is not clear that these fuels would have equivalent equilibrium deposit thickness. In the light of the results found, it was concluded that the presence of condensed phase fuel in the intake manifold increases CCD. Further, CCD can be significantly reduced by increasing the FACT and ensuring that equilibrium is approached in the intake manifold (increased vaporization). It was also concluded that for a warm engine HEPHAG type fuels can be burned without excessive CCD at equilibrium engine operating condition. However, temporarily cold manifold conditions (cold starts) may significantly increase long term CCD formation. The data indicate that the most crucial fuel components in deposit formation are the very last of the high boiling fractions. (ERA citation 07:042692)