Performance and NO_x Emissions of Spark Ignited Combustion Engines Using Alternative Fuels—Quasi One-Dimensional Modeling II. Methanol Fueled Engines

Abstract

A thermodynamic model employing a one-dimensional semi-empirical flame speed has been used to evaluate methanol as a reciprocating engine fuel. The empirical parameters in the flame speed were determined by matching computed combustion durations with experimental values' reported in the literature. Satisfactory agreement was obtained between predicted and measured values for power, efficiency and NO_x emissions.

The model predicts maximum thermal efficiency of the methanol engine for equivalence ratios in the 0.7 to 0.8 range. This is within practical operating range, as experiments have shown the lean misfire limit to be near an equivalence ratio of 0.6. NO emissions are predicted to reach a maximum near an equivalence ratio of 0.9, and are reduced by about two-thirds at an equivalence ratio of 0.75. Addition of water to methanol is shown to significantly reduce NO_x emissions, although with some loss in thermal efficiency. Improved fuel economy without excessive NO_x emissions can be obtained by employing methanol-water blends at high compression ratios.