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The present study investigated three techniques for predicting combustion chamber deposit formation in a direct injection diesel engine. One non-intrusive technique, based on the factorial experimental design method was used to develop an empirical model. This model predicts deposit weight as a function of time, but is dependent on engine type, type of lubricating oil, and engine operating parameters. Two intrusive techniques were also investigated for predicting deposit formation: a fast response thermocouple and a deposit conductivity probe, both being located within the combustion chamber. It was shown that the fast response thermocouple technique provided a correlation between in-cylinder peak temperature phase lag and deposit thickness. The conductivity probe correlated electrical conductivity with deposit growth. As well, the waveform characteristics from the conductivity probe showed the potential to predict the physical structure of the deposits.

This paper describes an experimental study to determine the potential for fuel efficiency improvements offered by dedicated, high compression E85 engines with optimized powertrain calibration strategies. The study involved a prototype variable fuel engine that could operate using either gasoline or E85, and a high compression version of the same engine that was suitable only for E85. Fuel consumption and engine-out emissions were evaluated using steady-state engine dynamometer tests to represent urban and highway speed/load conditions. For each fuel and engine combination, the fuel efficiency and emissions trade-offs provided by varying Exhaust Gas Recirculation (EGR) levels were determined. For the high compression engine, operation at lower speed/higher load conditions (producing the same power as the standard speed/load settings) was also investigated.

This paper describes an experimental study comparing the peak ignition voltage requirements of natural gas and gasoline in a typical bi-fuel vehicle application. Chassis dynamometer tests were carried out in which the vehicle was subjected to different types of transient wide open throttle events to create “worst case” voltage requirements. In addition to measurements of ignition voltage, other factors known to influence voltage requirements (such as cylinder pressure, electrode temperature, and fuel/air ratio) were recorded during the transient tests in order to obtain a better understanding of the underlying reasons for observed differences in voltage requirements between the two fuels and between the different transient test procedures. The results presented in this paper quantify the increased peak voltage requirements (relative to gasoline) for reliable ignition of natural gas under various operating conditions.

In addition to the Spark Ignited and Compression Ignited modes of reciprocating internal combustion engine operation, a third option exists. In this class of engine, elevated charge temperatures and (in some cases) active chemical species are employed to achieve a Homogeneous Charge Compression Ignition (HCCI) mode of operation. This is typically accomplished using copious amounts of charge dilution by exhaust gases, which can elevate charge temperatures into autoignition regimes, yet simultaneously temper runaway combustion rates which would otherwise lead to destructive knocking. Engine operation in the HCCI mode has been described as efficient, stable, and low in the production of engine-out emissions. However, with the large amounts of charge dilution required, such engines to date suffer from relatively low energy density, and are difficult to control over wide ranging speed/load conditions.

This paper describes experimental studies carried out as part of a program to develop a neat methanol (M100) version of a GM 4-cylinder light truck engine. The engine was originally intended for variable fuel applications with fuels containing up to 80% ethanol. To permit M100 operation, a variable energy ignition circuit and special recessed surface gap ignitors have replaced the standard ignition components. This is referred to as a “plasma jet” ignition system, and is employed both to overcome the cold starting difficulties inherent with neat alcohol fuel and to permit less enrichment to be used during start-up in the interest of reduced hydrocarbon emissions. The plasma jet ignition systems used in previous related studies suffered from excessively high ignition energy requirements which would be detrimental to ignitor durability.