Ignition delay time

The time from initiation of reaction (marked as the end of compression in Fig. 6.7) to the maximum rate of pressure rise in the first stage, which corresponds to the maximum in an accompanying light output, is defined as Ti. The interval from this point to the maximum rate of pressure rise in the second stage is defined as t2- When the variation of these parameters is plotted as a function of the isentropically compressed core gas temperature (see Section 6.3.5) it is found that ti decreases monotonically with increasing temperature, whereas t2 increases at first, before decreasing 

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The electrical energy is rapidly transformed into thermal energy, and because the temperature of the ionized gas is generally above 300 K, the ignition delay time is short compared with the spark duration, . Ignition only takes place if the electrical energy exceeds the critical value, and if this energy is... 

For Hquid fuels, ignition delay times are of the order 50 ]ls at 700 K and 10 ]ls at 800 K. At low temperatures most of the ignition delay is the result of slow, free-radical reactions, and a distinction between the initiation and explosion periods within the ignition delay time can be made. With increasing ignition temperature for a given mixture, these times become comparable and at temperatures as high as 1500 K, both times may be of the order of lO " s. Consequently, the reaction zone in the flame of a mixture is observed to be one continuous event (12—14). 

DEE eombustors have pre-mix modules on the head of the eombustor to mix the fuel uniformly with air. To avoid auto-ignition, the residenee time of the fuel in the premix tube must be less than the auto-ignition delay time of the fuel. If auto-ignition does oeeur in the pre-mix module then it is probable that the resulting damage will require repair and/or replaeement of parts before the engine is run again at full load. 

If auto-ignitions occur, then the design does not have sufficient safety margin between the auto-ignition delay time for the fuel and the residence time of the fuel in the pre-mix duct. Auto-ignition delay times for fuels do exist, but a literature search will reveal that there is considerable variability for a given fuel. Reasons for auto-ignition could be classified as follows ... 

A flammable vapor flows tlu ough a 2-inch-insulated pipe at a flow rate of 4.5 acfm. A lagging fire started and heated a 4-foot lengtli of the pipe to 150 °F, vvliich is above tlie ignition temperature of tlie vapor. The ignition delay time of tlie vapor is e.xpressed by... 

The residence time of tlie vapor in the pipe section is less than tlie ignition delay time. Therefore, ignition will not take place. 

Lu, Vyn, Sandus and Slagg (Ref 17) conducted ignition delay time and initiation studies on solid fuel powder-air mixts in an attempt to determine the feasibility of solid-air detonations. The materials investigated included Al, Mg, Mg-Al alloy, C and PETN. Ignition delay time was used as a method of screening the candidate fuels for further work in initiation studies which determined detonation wave speed, detonation pressure, detonation limits, initiation requirements, and the effect of particle size and confinement. The testing showed the importance of large surface area per unit mass, since the most... 

Inspection of the numerical solutions of the equations shows that, with the exception of Es= 0 kcal/mole, the rate of surface temperature increase with time is very large once the surface temperature reaches approximately 420°K—on the order of 108°K/sec. Because typical autoignition temperatures are of the order of 625°K for composite propellants, the particular value of the ignition temperature does not affect the computed numerical value of the ignition-delay time. 

Parametric studies showed that mass diffusion in the gas phase could be neglected under most conditions. The calculations also show that the selection of the hypergolic combination (i.e., the gaseous oxidizer and the propellant system) fixes all of the parameters except the initial temperature and the oxidizer concentration. A general solution of the model shows that the ignition-delay time is approximately rated to the gaseous oxidizer concentration by the relation... 

Gas density Propellant density Boltzmann constant A factor to account for temperature oscillations ignition delay time Diffusion time... 

The explosive decomposition of the solid has been studied in detail [6], The effect of moisture upon ignitibility and explosive behaviour under confinement was studied. A moisture content of 3% allowed slow burning only, and at 5% ignition did not occur [7], Thermal instability was studied using a pressure vessel test, ignition delay time, TGA and DSC, and decomposition products were identified [8], The presence of acyl chlorides renders dibenzoyl peroxide impact-sensitive [9], There is a further report of a violent explosion during purification of the peroxide by Soxhlet extraction with hot chloroform [10], Residual traces of the peroxide in a polythene feed pipe exploded when it was cut with a handsaw [11]. The heat of decomposition has been determined as 1.39 kJ/g. The recently calculated value of 69° C for critical ignition temperature coincides with that previously recorded. 

Cetane number a number indicating the ignition quality of diesel fuel a high cetane number represents a short ignition delay time the ignition quality of diesel fuel can also be estimated from the... 

The smoke characteristics and the ignition capabilities of igniters are evaluated by using a micro-rocket motor. Ignition delay time and rate of pressure rise are... 

It predicts ignition delay times for space rocket engines and ignition pressure spikes (Ref 40)... 

Japan 1967, 28(2), 154—58(Japan) From CZ 1968(42), Abstr No 2922 CA 70, 49151j (1969) (Explodability of AN-metal powd systems was investigated by means of shock-sensitivity tests and the Knipp Ignition Test. The results were dependent on the type of metal. The ignition point decreased in the order of metals Znactivation energy of the ignition reaction was ealed from die ignition-delay-time at different temps)... 

NPN mixtures in air, the picture is less clear. One possibility is that only the reduction of ignition delay time caused by the addition of nitrite and nitrate improves the coupling between the shock front and combustion zone. 

No explanation is offered for the peculiar fractional power dependence of the ignition delay times on fuel or oxygen concn. Nor is there any comment on what appears to be a low... 

Investigation of the Ignition Delay Times for Propylene Oxide-Oxygen-Nitrogen Mixtures ,... 

Temp, °F Igniter Delay Time, secs Change, %... 

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