Water Addition to Gasoline-Effect on Combustion, Emissions, Performance, and Knock 820314

A single cylinder engine was used in studies to determine basic combustion, emission and performance characteristics of water-gasoline mixtures, with water introduced to the intake manifold as a liquid or a vapor. Measurements on ignition delays, combustion intervals, power, exhaust temperature, knock and exhaust emissions were made over a range of operating conditions. Test conditions which included several values of speed, engine air flow, spark timing, mixture ratio and water addition rate were chosen to isolate effects of individual parameters and as such are not typical of conditions used with practical engine systems. The results of this basic study were used to determine the effects of water and its state of matter on the measured parameters.

With respect to gasoline, water-gasoline mixtures have slower burn rates, with both ignition delay periods and combustion intervals being longer. Minimum advance for best torque (MBT) spark timings are advanced relative to gasoline values. Knock limited spark advance is extended with water addition. Power at constant equivalence ratio and engine airflow is decreased while fuel and energy consumption are increased. Water has virtually no effect on CO concentration in exhaust gases and has a slight effect on HC concentrations. A small decrease in HC concentration is observed at water levels below the saturation limit of air but an increase occurs at higher levels. The concentration of NO is decreased with added water. Lean limits of operation are compromised.

Due to the high latent heat of vaporization of water, the magnitude of effects on combustion and emissions is much larger with water as a liquid than as a vapor.