Study On The Mechanism Of The Effect Of Ignition Delay On The Combustion Characteristics In Wide Speed Range Of Scramjet

One of the core difficulties of scramjet combustor is ignition and combustion.A large number of studies have shown that different fuels have great influence on the combustion performance of supersonic combustors because of their different physical and chemical characteristics.The ignition delay time of fuel is one of the most important parameters to study the kinetic characteristics of fuel chemical reaction,which has a very important impact on combustion performance.However,the current research on fuel selection only focuses on the existing or commonly used fuels in nature,and the understanding of the mechanism of ignition delay on combustion characteristics is very limited.Therefore,it is necessary to study the mechanism of the effect of continuously variable ignition delay on combustion performance.At the same time,scramjet with wide-speed flight has become the current research trend.Previous studies only focus on single flight condition,which requires more stringent combustion requirements: reliable ignition and high-performance combustion need to be achieved in a wide range of inflow velocity,temperature and pressure combustion chamber environment.Therefore,in order to meet the requirements of wide-speed flight,the scramjet engine with wide-speed flight range is required to achieve reliable ignition and high-performance combustion.It is necessary to study the mechanism of the effect of continuously variable ignition delay on combustion performance in a wide speed range.In this paper,Hyshot-II,which has detailed flight data,is selected as the benchmark model for the study.The fuel ignition delay model of scramjet is constructed by using uncertainty quantitative analysis method.A series of numerical calculations are carried out by RANS method.The specific research contents and results are as follows:Firstly,based on the uncertain quantitative analysis method,a fuel ignition delay time model is established,and the results calculated by CHEMKIN software are compared and analyzed.It is found that the ignition process is in good agreement,which shows the reliability of the model.Secondly,based on the model of fuel ignition delay,the relationship between fuel ignition delay time and supersonic combustion performance,i.e.fuel ignition delay time-combustion efficiency characteristic curve,is established.The results show that with the increase of ignition delay time,there are two distinct inflection points of combustion efficiency,which constitute three different characteristic regions,named limit zone,sensitive zone and critical zone respectively.It shows that the characteristics of ignition delay time of fuel play different roles in regulating combustion performance.It is found that the characteristics of combustion efficiency with ignition delay time are not changed by using dual-hole jet.Finally,the influence of inflow Mach number on combustion performance is preliminarily studied in the wide Mach number range,that is,the influence of total inflow temperature on combustion performance.It is found that with the decrease of Mach number in flight,the combustion efficiency limit can be further improved,and the ignition delay has an increasing influence on combustion performance.When the total temperature of incoming flow is lower than a certain temperature(1400K),there will be a mode transition phenomenon of heat congestion.By improving the current level of hydrocarbon fuel to shorten the ignition delay time,the maximum combustion efficiency gain of 55.4% can be achieved.In this paper,the mechanism of the effect of ignition delay on combustion performance in wide speed range is studied,and a complete understanding of the regulation of combustion performance of fuel is preliminarily established.The innovation of this paper is that based on the application of uncertain quantitative analysis to build the fuel ignition delay time model,the inherent regulation law of combustion characteristics based on fuel ignition delay time in wide speed range is preliminarily obtained.