Investigation Of Knocking Control Of Direct Injection Piston-type Aviation Kerosene Engine

Piston-type aviation kerosene engine is getting more and more attention in recent years.One reason is that piston-type engine has small size,high power to weight ratio and low cost.Another reason is that comparing with gasoline,kerosene is not easy to volatilize,and with low flash point,which means higher safety.However,the octane number and auto-ignition temperature of kerosene is small,which make it easy to knock at heavy load.Hence,researching the methods to control knocking of piston-type aviation kerosene engine is of vital importance and significant engineering application value.In this paper,dual spark ignition and two-stage injection were conducted on a low-pressure air-assist direct injection engine.In addition,sensitiveness of relevant factors such as the mixture concentration,ignition timing,and compression ratio was analyzed.Research results show that:Dual spark ignition with simultaneous ignition cannot suppress the knocking of aviation kerosene,and it even makes it worsen.However,if spark timing is delayed at the same time,the knocking intensity will be decreased.Considering the ignition energy of simultaneous ignition is too big,method of asynchronous ignition is carried out.And the result is dual spark ignition with asynchronous ignition is effective to restrain the knocking of aviation kerosene.The main reason is that the spark of the second spark plug can ignite the end gas before it self-ignites,and this prevents the generation of knocking.In two-stage injection mode,mixture around spark plugs is rich,which can quicken the rate of flame propagation,and mixture at the end of the chamber is lean,which is hard to self-ignite.So this method is effective.However,the delay of the injection timing and the increase of the proportion of the second injection will worsen the atomization of the fuel and the uniformity degree of mixture.And this is not good for the thermal efficiency,power and the emission performance.Both two-stage injection and dual spark ignition have disadvantages,but analysis found that the combination of the two methods could offset the disadvantages.Moreover,experimental results verified this idea.The main reason is simultaneous ignition firstly ignites the rich mixture around the plugs,which solves the incomplete combustion in this field,and makes flame propagation rate faster.Hence,the end gas cannot ignite spontaneously.In addition,the sensitivity analysis turns out that decreasing compression ratio can effectively suppress the knocking combustion of aviation kerosene,while the mixture concentration influences knocking intensity the least.