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A detailed chemical kinetic mechanism for hypergolic ignition of N2H4/NO2 gas mixture at low temperatures has been constructed. In this mechanism, the hypergolic ignition is caused by following sequential reactions of H atom abstraction from N2Hm by NO2. N2H4 + NO2 = N2H3 + HONO or HNO2 (R1) N2H3 + NO2 = N2H2 + HONO (R2) N2H2 + NO2 = N2H + HONO (R3) N2H + NO2 = N2 + HONO (R4) These reactions are exothermic, especially heat release by the reaction (R4) is large because of N2 production. Temperature rise caused by the heat release accelerates the initiation reaction (R1). This 'thermal feedback' is responsible to the hypergolic ignition at ambient temperatures. Since no experimental and theoretical information was available on these reactions, rate coefficients were evaluated on the basis of transition state theory, unimolecular rate theory, and master equation analysis with quantum chemical calculations of potential energy curves. Results of simulations by using the present mechanism including reactions (R1)-(R4) reasonably agree with existing experimental data.

T work is concerned with the ignition of hypergolic liquids at various pressures, and attempts to simulate timetemperature relationships in a droplet before it bursts into flame. It is known ~ that the ignitibility of a propellant can be affected drastically by changes in pressure, as well as temperature and the geometry of the enclosure surrounding the impinging streams of reactants. But the reasons for this sensitivity are not clear, nor is it known whether liquid particles that differ in size also differ in ignition behavior. At atmospheric pressure, two liquids that comprise a hypergolic mixture burst into flame almost as soon as they meet. At lower pressure there is longer delay before ignition occurs. Then, below some pressure, ignition does not occur, even though slightly above this point the hypergolic mixture does ignite after a reasonable delay time. The pressure at which cut-off occurs, marking the boundary between ignition and nonignition, is not well defined and reproducibility becomes increasingly more difficult as the pressure is reduced.

Reaction of hydrazine and nitrogen tetroxide at pressures of .001 mm hg in a steel vacuum tank

Small rocket engine tests were conducted for the purpose of obtaining pulse performance data to aid in preliminary design and evaluation of attitude control systems. Both monopropellant and hypergolic bipropellant engines of thrust levels from 1 to 100 lbs were tested. The performance data for the hypergolic propellant rockets are compared with theoretical performance calculated from idealized chamber filling and evacuation characteristics. Electromechanical delays in valve response and heat transfer characteristics were found to cause substantial deviation between theoretical and test performance. The theoretical analysis is modified to obtain a semi-empirical model for hypergolic propellant rockets which is demonstrated to be reasonably accurate for two different engine configurations over a considerable range of duty cycles.

Random high amplitude short duration (less than a millisecond) pressure and accelerometer disturbances were observed with the hypergolically fueled Apollo Spacecraft engines during their development phase. These disturbances, called pops, were and are undesirable because they may trigger damaging combustion instability. In all instances the pops were either eliminated or reduced to acceptable levels through trial and error testing since there were no design criteria by which logical element or pattern changes could be made. Generally, the pops were attributed to random accumulation and mono-propellant explosion of fuel pockets or zones caused by such things as poor element or pattern design, orifice flow instabilities (hydraulic flip), plugged oxidizer orifices, or fuel leakage through weld cracks. Although these postulated causes are certainly possible, recent investigations (Refs. 1-5) suggest that most of the observed pops are related to combustion phenomena associated with unlike hypergolic propellant stream impingement. For instance it has been shown (Ref. 1) that small local explosions of mixed fuel and oxidizer, rather than monopropellant fuel explosions, are most likely the source of pop triggers. On the basis of these investigations a semiempirical model has been developed which relates these small local hypergolic stream explosions to the occurrence of pops. This model was used to correlate development testing pop data obtained from the Apollo Lunar Module (LEM) ascent engine injectors, the Apollo Service Module (SPS) engine injectors, an advanced research SPS injector (SPS-IOS), and a NASA Jet Propulsion Lab. combustion research engine injector. The resultant correlations were used to predict injector pattern changes which successfully eliminated the popping observed previously with the advanced research SPS-IOS injector. The pop model is based on the supposition that the small local explosions which occur within the impingement region of unlike hypergolic propellant streams act to trigger unburned spray detonations which produce transient pressure and accelerometer spikes that are identified as pops. The basis for this hypothesis lies in two basic pieces of experimental work reported in Refs. 1 and 2. The supposed relationship between the small local explosion and the observed pop is illustrated in Fig. 1. It is postulated that the small local explosion emits a spherical blastwave which can initiate detonation of the adjacent

A paper by Per lee et al. on the vacuum ignition of hypergolic propellants (hard start) has led to some interesting thoughts which may lead to a possible solution of this problem. The results of Perlee et al. indicate that hydrazine, A-50, and monomethyl hydrazine yield nitrates characteristic of their own basic compounds. Their paper also shows that another derivative of hydrazine (UDMH) yields ammonium nitrate (AN). The reasons for AN formation have not been determined. The explosive potential of AN has been found to be the lowest of the four nitrates investigated. Friedman et al. found that dried ammonium nitrate did not decompose under hard vacuum when heated to 300°C, but was relatively stable when dried under vacuum conditions; only after water vapor had been added and heated gradually to 180°C did decomposition commence. Having taken a preliminary look at this problem, I find a trend that indicates that there is a correlation between the concentration of the alkali impurities in the propellants and the formation of ammonium nitrates, which are the least potentially hazardous of the nitrates. Perlee's infrared data show that AN is formed only in the UDMH system. In repeated testing of production samples of the above fuels, UDMH exhibited significantly larger quantities of alkalimetal impurities than any of the other fuels. Table 1 shows the findings of the various investigators who have published data on these systems. It is interesting, therefore, to speculate that these impurities may act as catalysts in the oxidation processes which ultimately produce the ammonium nitrates. Alternatively, if certain of these impurities (e.g., Na and Li) are added in sufficient quantities, they may decompose the nitrate without