Experimental Study On The Effect Of Nanosecond Pulsed Plasma On Combustion Of Methane-Air Mixture

With the increasingly stringent emission regulations,internal combustion engines are developing in the direction of high thermal efficiency and low emissions.The application of technologies such as high compression ratio,lean combustion,and low-temperature combustion has worsened the ignition and combustion conditions in the cylinder.Traditional ignition coil ignition can no longer meet the requirements.Therefore,it is necessary to explore new ignition methods.Nanosecond Pulse Discharge(NPD)can generate high-energy active ions,and it has become more and more widely used in plasma-assisted combustion,pneumatic flow control,and material surface treatment.The use of NPD ignition can not only effectively improve the engine Lean burn limit,reduce combustion pollutant emissions,and controllable combustion can be achieved by changing the discharge parameters of the ignition system.Therefore,based on a compact high-repetition frequency nanosecond pulse generator,this paper studies the effect of nanosecond pulse discharge plasma on the combustion of methane-air mixture in a constant volume combustion bomb.This paper has completed the overall design and construction of the constant volume incendiary bomb test bench,and developed a software and hardware control system around the test bench and the discharge system.The analysis results of the output characteristics and discharge characteristics of the nanosecond pulse power supply show that the output characteristics of the pulse power supply have a greater impact on the breakdown characteristics of the electrode terminals.The output voltage rise rate of the pulse power supply affects the maximum breakdown voltage.The higher the breakdown voltage,the shorter the discharge duration;the peak output voltage of the pulse power supply will affect the breakdown current.The higher the output voltage peak,the greater the maximum breakdown current,and the peak breakdown voltage remains basically unchanged;when multiple discharges are used During the pulse,the first pulse has a higher breakdown peak voltage and higher discharge energy.After the second pulse,the maximum breakdown voltage and discharge energy are reduced.The shorter the pulse interval time,the coupling relationship between adjacent pulses.The larger the value,the lower the peak breakdown voltage.As the pulse interval increases,the discharge energy will gradually increase and converge to the first discharge pulse.The study on the minimum ignition energy of NPD shows that the minimum ignition energy of NPD ignition is less than ignition coil ignition at different mixture concentrations;and NPD ignition can expand the lean burn limit.When λ=2.0,traditional ignition coils cannot successfully ignite methane-air.The NPD can still achieve a 100%ignition success rate by increasing the number of pulses(PN).The ignition success rate is greatly affected by the initial temperature of the mixture,and the increase in temperature can greatly reduce the minimum ignition energy.After ignition near the ignition energy,the combustion stability will decrease,the position and shape of the fire nucleus will be unstable,and the combustion cycle will fluctuate greatly.The research on the discharge channel,initial fire core and flame development under different discharge parameters of NPD shows that by increasing the discharge energy,NPD will cause the discharge channel to develop in the vertical direction of the electrode,forming an approximate spherical shape.When NPD is ignited,the initial fire core radius and the flame development speed gradually increases with the increase of the number of pulses,and presents a change law of first increasing and then decreasing with the increase of the pulse interval.The compression wave generated by the NPD discharge will change the shape and location of the initial fire nucleus,and the shape of the initial fire nucleus mainly half-moon and elliptical.Under the lean mixture,the pulse will be divided into two independent fire nuclei,and different degrees of displacement will be produced as the pulse intensity changes;the initial temperature of the mixture will increase the flame propagation.At the same time,the airflow movement generated by NPD ignition after the temperature is increased is no longer obvious.In the lean mixture,the ignition effect of the ignition coil is weaker than that of the NPD ignition,and NPD ignition has a larger combustion adjustment space.The increase in temperature will expand the pulse interval(Pulse Interval,PI)coupling time range,so that NPD can also be achieved at low frequencies Better ignition effect;different discharge modes and discharge parameters have little effect on the maximum combustion pressure and pressure rise rate,but have a greater impact on ignition delay and combustion duration.The number of pulses during NPD ignition mainly affects the ignition delay,and the pulse interval mainly has a certain effect on the combustion duration.As the number of pulses increases,the maximum change in ignition delay exceeds 50%.