Ignition processes and characteristics of charring conductive polymers with a cavity geometry in precombustion chamber for applications in micro/nano satellite hybrid rocket motors

The arc ignition system based on charring polymers has advantages of simple structure,low ignition power consumption and multiple ignitions,which bringing it broadly application prospect in hybrid propulsion system of micro/nano satellite.However,charring polymers alone need a relatively high input voltage to achieve pyrolysis and ignition,which increases the burden and cost of the power system of micro/nano satellite in practical application.Adding conductive substance into charring polymers can effectively decrease the conducting voltage which can realize low voltage and low power consumption repeated ignition of arc ignition system.In this paper,a charring conductive polymer ignition grain with a cavity geometry in precombustion chamber,which is composed of PLA and multiwall carbon nanotubes(MWCNT)was proposed.The detailed ignition processes were analyzed and two different ignition mechanisms in the cavity of charring conductive polymers were revealed.The ignition characteristics of charring conductive polymers were also investigated at different input voltages,ignition grain structures,ignition locations and injection schemes in a visual ignition combustor.The results demonstrated that the ignition delay and external energy required for ignition were inversely correlated with the voltages applied to ignition grain.Moreover,the incremental depth of cavity shortened the ignition delay and external energy required for ignition while accelerated the propagation of flame.As the depth of cavity increased from 2 to 6 mm(at 50 V),the time of flame propagating out of ignition grain changed from 235.6 to 108 ms,and values of mean ignition delay time and mean external energy required for ignition decreased from 462.8 to 320 ms and 16.2 to 10.75 J,respectively.The rear side of the cavity was the ideal ignition position which had a shorter ignition delay and a faster flame propagation speed in comparison to other ignition positions.Compared to direct injection scheme,swirling injection provided a more favorable flow field environment in the cavity,which was beneficial to ignition and initial flame propagation,but the ignition position needed to be away from the outlet of swirling injector.At last,the repeated ignition characteristic of charring conductive polymers was also investigated.The ignition delay time and external energy required for ignition decreased with repeated ignition times but the variation was decreasing gradually.

A review on ignition characteristics of arc faults in wire system of aircraft

The development of aircraft electrification can improve energy utilization efficiency and reduce the green gas emissions,which is the future trend.However,aircraft electrification would increase the probability of arc faults in the wire system.Arc can ignite the combustibles by the arc column or hot droplets,which has high fire risks.Arc faults have triggered several catastrophic aeronautical accidents in the past.Electrical fire safety is a top priority of aircraft in the future.An in-depth understanding of the arc fault ignition mechanism plays a crucial role in preventing arc fires and optimizing wire layout.This review article performs a comprehensive summary of relevant research concerning the fire risks of arc faults,the causes of arc faults in the wire system,and the ignition behaviors of arc faults.The main findings regarding the direct ignition of arc faults and ignition of hot droplets are emphasized.The arc ignition characteristics in existing research are firstly summarized,including the arc ignition experiment platforms and thermal hazard characteristics of arc faults.Additionally,the generation,impacting process,and ignition characteristics of hot droplets are then presented.Finally,the limitations in existing research about ignition characteristics of arc faults are also outlined,while identifying the future research needs of fires caused by arc faults.

Investigation on ignition characteristics of charring conductive polymers stimulated by electric energy

The arc ignition based on charring conductive polymers has advantages of simple structure,low ignition power consumption and restart capacity,which bringing it broadly application prospect in hybrid propulsion system of micro/nano satellite.In order to optimize the performance of arc ignition system,it is essential to have a deeper understanding of the ignition processes and ignition characteristics of charring conductive polymers.In this paper,the thermal decomposition,electrical conductivity and thermal conductivity characteristics of charring conductive polymers with different conductive additives and matrix materials were comprehensively evaluated.An experimental investigation was conducted to determine the ignition behaviors and characteristics of different charring conductive polymers in a visual ignition combustor.The experiment result showed that the ignition delay and external energy required for ignition are negatively correlated with voltage and initial temperature of the ignition grain,but positively correlated with oxidizer flow velocity.Compared with charring conductive polymers containing multi-walled carbon nanotube,the ignition delay of charring conductive polymers with carbon black is significantly higher and the pyrolysis time is relatively longer.However,the ignition and initial flame propagation of charring conductive polymers with carbon black is more violent and more inclined to carbon particle ignition.Finally,the restart characteristic of different charring conductive polymers was studied.The ignition delay and external energy required for ignition of different charring conductive polymers all reduced with the increasing of the number of ignitions.However,the ignition characteristics would not change a lot after repeated ignition.

Experimental investigation of a gliding discharge plasma jet igniter

Relight of jet engines at high altitude is difficult due to the relatively low pressure and temperature of inlet air.The penetration of initial flame kernel affects the ignition probability in the turbine engine combustor greatly.In order to achieve successful ignition at high altitude,a deeper penetration of initial flame kernel should be generated.In this study,a Gliding Arc Plasma Jet Igniter(GAPJI)is designed to induce initial flame kernel with deeper penetration to achieve successful ignition at high altitude.The ignition performance of the GAPJI was demonstrated in a model combustor.It was found that GAPJI can generate plasma with deeper penetration up to 30.5 mm than spark igniter with 22.1 mm.The discharge power of GAPJI was positively correlated with flow rate of the carrier gas,approaching 200 W in average.Ignition experiments show that GAPJI has the advantage of extending the lean ignition limit.With GAPJI,the lean ignition limit of the combustor is 0.02 at 0 km,which is 55.6%less than that with spark igniter(0.045).The evolution of flame morphology was observed to explore the development of the flame kernel.It is shown that the advantage of a high penetration and continuous releasing energy can accelerate the ignition process and enhance combustion.