Numerical Research Engine Coolant Temperature and Flow Rate Effect on the Engine Cold Start

Abstract

To study the influence of LNG fuel supply system on engine cooling system, ensure that the engine cold start performance, an AMESim based LNG fuel supply system simulation model with the key components of vaporizer was proposed. By analyzing the influence of the coolant temperature and flow rate on the phase transition of LNG, and worked out the ranges of temperature and flow rate in vaporizer when the engine reached normal operating. It has a strong significance to the design of LNG fuel supply system. Keywords-vaporizer; coolant; flow rate; temperature LNG fuel supply system must provide sufficient quantity and characteristics in full working condition to assure the high control accuracy of fuel to the LNG engine as well as the transient behavior and cold start. The optimum matching of fuel system and cooling system was one of the key techniques to realize this objective, that is to say, the liquid from the LNG storage tank through the fuel supply system must absorb enough heat to meet the requirements of latent heat of vaporization phase change, to ensure that engine performance standards. Fuel of LNG vehicle was stored in the form of cryogenic liquid, but it must be gas state when supplied to the engine. Therefore, vaporizer was a key component in the LNG vehicle fuel system. The important role of the vaporizer was to heat the liquid fuel in low-temperature, and then supplied to the engine. General coolant was circulated to vaporize LNG in car vaporizer (1). LNG vaporizer was a typical small shell and tube structure, it was connected in the engine cooling system, and the countercurrent heat exchange working principle was used to heat LNG or the mixture of LNG and natural gas. The fuel gas pressure was generally required 0.3~1.0MPa in between before into the engine, the temperature allowed 233K ~363K in between. If the intake air temperature was too high, which may lead to explode of natural gas engine, and then it was difficult to achieve the maximum power; but if the intake air temperature was too low, it may cause surging engine and off- ignition. The volume of fuel gas flow rate was controlled by the engine inlet valve, under the case that gas pressure was stability, and the fuel gas density was directly affected by gas temperature, in this way it affected the quality of gas entering the engine. The gas flow rate and temperature were mainly determined by the vaporizer. Therefore, in this article simulation was used to study the influence of coolant temperature and flow rate on phase transformation of LNG. Through optimizing system parameters to give the design of LNG engine fuel supply system. Research the influence of LNG fuel supply system to the engine cooling system, and ensure the performance of engine cold start.