The effects of fuel evaporation on engine knock

It has been known for a long time that alcohol-gasoline blended fuels exhibit an unexplained tendency to knock at high engine speeds; a characteristic that is not generally experienced with conventional gasoline. Early studies showed that the problem could be linked to an unusually high temperature sensitivity exhibited by the blended fuels, but the exact cause of this temperature sensitivity was not readily identified, and research efforts became diversified in attempts to make headway. Initial studies in the field of high-speed knock were based on the assumption that a chemical reaction sensitivity to temperature was the root cause. It is now suspected that the effect may be due to a thermal manifestation of the variation in evaporative cooling characteristics of different fuels at different engine speeds. Research findings leading up to the present project have indicated that the high-speed knock phenomenon could be explained by the influence on the overall mixture temperature of the thermal-evaporative behaviour of a fuel during the inlet process. The thermal-evaporative behaviour is very complex, however, and has been characterized only tentatively, as yet. The present project was initiated to study the effect of engine speed on the fuel evaporation behaviour and on the complex heat transfer processes that occur within the intake manifold of a spark-ignition engine. The primary aim of the project was to establish the temperature of the air/fuel mixture after the inlet process has been completed, and to identify how this temperature responds to changes in engine speed and fuel composition. The fuels investigated included conventional gasoline and gasoline-alcohol blends. It was anticipated that the findings of the project would enable the fundamental hypothesis concerning the basic cause of high-speed knock to be evaluated.

Grantor dc:publisher.institution

Department of Mechanical Engineering

Year dc:date.issued

1993

Author dc:creator

• Moran, Derek Paul

Advisor dc:contributor.advisor

• Yates, Andrew

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/8478

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/8478