Performance of Natural-Gas-Fueled Engines with Variable Intake-Manifold Temperatures

The possiblity of using an elevated intake-manifold temperature for lean-burn, turbocharged spark-ignition engines fueled by natural gas has been investigated. Experiments have shown that the power capacity, shaft efficiency and NO_x emissions could be maintained at the rated level if an increase in intake-manifold temperature was accompanied by an increase in air-to-fuel ratio. A higher air-to-fuel ratio is allowed with hotter mixtures since both the lean misfire limit and the volumetric efficiency appear to increase with increasing mixture temperature. An intake-manifold temperature at the level of the jacket-water temperature of the engine has the advantages of an easier control of the mixture temperature, a better energy utilisation in cogeneration systems and a better part-load efficiency of the engine.