An assessment methodology for fuel/water consumption co-optimization of a gasoline engine with port water injection

For the requirements of rigorous CO2 and emissions regulations, the water injection technique is a promising solution to improve fuel economy. The establishment of an optimum water injection strategy is still a challenge when this technique is applied as a method of thermal efficiency enhancement. The present study proposes an evaluation index for the energy conservation potential of water injection strategies, which optimizes water consumption and minimizes the negative influence on energy conservation. An evaluation approach based on Brent’s method is adopted to search the optimum combination parameters of objection function, in which constraints consider fuel cost, usage cost, and space cost. A comprehensive vehicle dynamics model is established and validated to evaluate the energy conservation potential of proposed water injection strategies. The results present the proposed index provides an effective approach to assessing the trade-off relationship between water and fuel consumption. The fuel cost strategy improves fuel economy by 5.2% along the WLTC driving cycle, but this strategy consumes a large amount of water (1.08 L/100 km). In contrast, the proposed usage and space cost strategies save water consumption to 0.58 L/100 km and 0.29 L/100 km, respectively, although their ability to fuel conservation reduces to 4.8% and 4.5%, correspondingly. The comparison results provide considerable guidance on the selection of water injection strategies for vehicle designers and customers according to their purposes and demands.