Preparation and performance evaluation of high density hydrocarbon fuel for liquid ramjet engine application.

With their unique operational characteristics, hybrid rockets can potentially provide safer, lower-cost avenues for spacecraft and missiles than the current solid propellant and liquid propellant systems. Classical hybrids can be throttled for thrust tailoring, perform in-flight motor shutdown and restart. In classical hybrids, the fuel is stored in the form of a solid grain, requiring only half the feed system hardware of liquid bipropellant engines. The commonly used fuels are benign, nontoxic, and not hazardous to store and transport. Solid fuel grains are not highly susceptible to cracks, imperfections, and environmental temperature and are therefore safer to manufacture, store, transport, and use for launch. The status of development based on the experience of the last few decades indicating the maturity of the hybrid rocket technology is given in brief.

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The scramjet combustor a vital component of scramjet engine has been designed by employing fuel injection struts. Several experimental studies have been carried out to evaluate the propulsive performance and structural integrity of the in-stream fuel injection struts in the connect-pipe test facility. As the mission objective of hypersonic demonstrator is to flight test the scramjet engine for 20 s duration, in-stream fuel injection struts which are designed as heat sink devices encounter hostile flow field conditions especially in terms of high thermal and high convective loads in the scramjet combustor. To circumvent these adverse conditions, materials like Niobium C-103 and W-Ni-Fe alloys have been used for the construction of struts and a number of tests have been carried out to evaluate the survivability of the in-stream fuel injection struts in the scramjet combustor. The results thus obtained show that the erosion of leading edges of the Stage-II fuel injection struts in the initial phase and subsequently puncturing of the fuel injection manifold after 10-12 s of the test are noticed, while the other stages of the struts are found to be intact. This deteriorating leading edges of Stage-II struts with respect to time, affect the overall propulsive performance of the combustor. To mitigate this situation, Stage-II struts have been designed as cooled structure and other Stages of struts are designed as un-cooled structure. Material of construction of struts used is Nimonic C-263 alloy. This paper highlights the results of the static test of the scramjet combustor, which has been carried out at a combustor entry Mach number of 2.0, total temperature of 2000 K, with an overall kerosene fuel equivalence ratio of 1.0 and for the supersonic combustion duration of 20 s. Low back pressure has been created at the exit of the scramjet combustor using ejector system to avoid flow separation.Visual inspection of the fuel injection struts after the test revealed that all the Struts are found to be thermo-structurally safe in the combustor environment except for minor erosion of the leading edges of the struts. Stage-II struts made of two-passage cooled configuration are found to be thermo-structurally safe. Although other stages of struts used in the test are of un-cooled configuration, they too are found to be safe and intact. This demonstrates the fact that they experience thermally benign flow conditions compared to Stage-ii struts in the scramjet combustor.

A discovery was made recently that the heat release would be very efficient if it is associated with detonation phenomenon. A detonation wave imparts high pressure to the products of combustion which in turn produces large propulsive power as a result of expansion through the propulsive element. This kind of pressure gain combustor is a new idea which is going to be incorporated in the futuristic propulsive devices. A representative air breathing propulsive system configuration powered by the continuous detonation wave engine is chosen for the present investigation. This includes understanding of various processes occurring in the air intake, isolator, rotating detonation wave engine and flow expansion system. A detailed numerical modelling and simulation based on steady 1-D flow have been carried out. This analysis gave insight into the overall propulsion system performance taking into consideration of the interaction between various sub systems.

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The development of a controller which can be used for engines used in armoured fighting vehicles is discussed. This involved choosing a state of the art reference common rail automotive Diesel engine and setting-up of a transient engine testing facility. The dynamometer through special real-time software was controlled to vary the engine speed and throttle position. The reference engine was first tested with its stock ECU and its bounds of operation were identified. Several software modules were developed in-house in stages and evaluated on special test benches before being integrated and tested on the reference engine. Complete engine control software was thus developed in Simulink and flashed on to an open engine controller which was then interfaced with the engine. The developed control software includes strategies for closed loop control of fuel rail pressure, boost pressure, idle speed, coolant temperature based engine de-rating, control of fuel injection timing, duration and number of injections per cycle based on engine speed and driver input. The developed control algorithms also facilitated online calibration of engine maps and manual over-ride and control of engine parameters whenever required. The software was further tuned under transient conditions on the actual engine for close control of various parameters including rail pressure, idling speed and boost pressure. Finally, the developed control strategies were successfully demonstrated and validated on the reference engine being loaded on customised transient cycles on the transient engine testing facility with inputs based on military driving conditions. The developed controller can be scaled up for armoured fighting vehicle engines.

Dynatnic phenomena in 'ratn-accelerator', a ramjet-i1l-tube concept for accelerating projectiles to ultra high velocities, have been investigated analytically atld compared with the experitnental investigations reported in open literature. nle projectile resembles tlle centrebodyof a conventional ramjet, but travels through a stationary tube filled witll a mixture of gaseous fuel atld oxidizer. nle energy release process travels with a projectile i1lside tlle accelerator tube. nle characteristics of subsonic combustion, thermally-choked mode of propulsion, which is capable of increasing tIle velocity up to Chaptnatl-Jouguet (C-J) detonation velocity of tlle propellant mixture used in ram-accelerator tube, have been studied. The ram-accelerator with a fIXed diffuser area ratio operates witIl different initial velocities for different propellatlt mixtures. Propellallt mixture with CO2 as diluent is used for velocity range -770-1150 tn/s; propellant mixture with nitrogen a.~ diluent is used for velocity range -925-1450 tn/s atld that with helium as diluent is used for velocity range -1500-2000 m/s. Mixtures of propellants witll different diluents in varying degree of proportions, giving rise to different acoustic and C-J detonation speeds, have been i1lvestigated to evaluate tlleir suitability in tlle ratn-accelerator divided i1uo several segments.