Combustion Pressure Research Articles

Nitrous Oxide/Ethanol Cylindrical Rotating Detonation Engine for Sounding Rocket Space Flight

There are few experimental studies on rotating detonation engines (RDEs) with liquid propellants. This study reveals the static thrust performance of a cylindrical RDE with ethanol and liquid nitrous oxide as propellants under atmospheric pressure. This RDE had an inner diameter of 40 mm, a maximum combustor length of 230 mm, a nozzle contraction ratio of 1.7, and a nozzle expansion ratio of 9.1. Nineteen experiments were conducted at total mass flow rates of 184–210 g/s, mixture ratios of 3.6–5.9, and combustion pressures of 0.35–0.46 MPa, resulting in a maximum detonation velocity of 1840 m/s (approximately 80% of the theoretical detonation velocity, 2251 m/s), maximum thrust at sea level of 294 N, and maximum specific impulse at sea level of 148 s. In addition, the maximum characteristic exhaust velocity, c*, was 1716 m/s, which was 99% of the theoretical value. The characteristic length of the combustion chamber at this time was 0.15 m. Since conventional rocket combustion requires 1.57 m to achieve the same c* efficiency, this study shows that detonation combustion can reduce the combustor size by 88%.

Functional energetic materials: Simple preparation of fluorinated materials to improve safety, preservation and energy release performance of energetic materials

Paraffin wax (PW) coatings are widely used in the military as the most effective way to reduce the sensitivity of energetic materials, but their inert nature is not conducive to energy release. In this work, paraffin-like fluorine-containing molecules (FPW) which are highly anticipated on a large scale were synthesized by combining crystalline units with fluorine units via a simple method. Core-shell Al@FPW was prepared for further characterization. FPW exhibits better lubrication and greater density (1.14 g/cm3 vs. 0.81 g/cm3) than PW, which can provide favorable guarantees for reduced friction sensitivity and increased energy density. The similar melting temperatures and crystallization enthalpies (168 J/g vs. 201 J/g) of FPW and PW are advantageous for mitigating the temperature sensitivity of nano-Al. Furthermore, the improved hydrophobicity of Al@FPW prevents further oxidation of the active metal, thereby enhancing the preservation of nano-Al. Moreover, the reaction process of Al@FPW was characterized by DSC-Tg. Notably, the combustion pressure, pressurization rate and calorific value of Al@FPW are significantly increased compared to Al@PW. Meanwhile, the ignition delay time is reduced by 83 % and the combustion rate is increased by 330 %, which is attributed to the action of fluorine during the reaction. The exceptional performance of FPW holds great potential for replacing PW in various applications.

Experimental investigation on the effect of diesel-ethanol blends for a constant-speed diesel engine

ABSTRACT Keeping the need for energy security and the world’s transition to a thriving low-carbon economy in mind, the research, on the feasibility of diesel ethanol blends, has gained momentum. The present work is related to comparing the performance and emission characteristics of pure diesel [D100] with 4 diesel-ethanol blends [D90E10, D85E15, D80E20 and D75E25]. The single-cylinder 4-stroke un-modified diesel engine running at constant 1500 rpm was used for experimentation which ran at different loads. Experimental results showed that with the addition of ethanol in blends, the brake thermal efficiency (BTE) and exhaust gas temperature (EGT) reduced while brake-specific fuel consumption (BSFC) increased. The addition of ethanol shortened the combustion duration. Hence, D75E25 showed a rapid rise in combustion pressure and heat release rate (HRR). As the concentration of ethanol increases in blends, the oxide of nitrogen (NOx) is reduced and carbon monoxide and hydrocarbon (HC) are increased. Thus, D75E5 was good blend producing less NOx with the penalty of fuel consumption on an unmodified diesel engine. In the long run, the effect of blends on the engine should be checked to make ethanol a feasible fuel for diesel engines. Abbreviations: CA: Crank Angle; ATDC: After Top Dead Centre; BMEP: Brake Mean Effective Pressure; BSFC: Brake Specific Fuel Consumption; BTE: Brake Thermal Efficiency; BTDC: Before Top Dead Centre; CO: Carbon Monoxide; COV: Coefficient of Variation; D100: 100% Diesel + 0% Ethanol, Pure petroleum diesel; D90E10: 90% Diesel + 10% Ethanol; D85E15: 85% Diesel + 15% Ethanol; D80E20: 80% Diesel + 20% Ethanol; D75E25: 75% Diesel + 25% Ethanol; HC: Hydrocarbon; IMEP: Indicated Mean Effective Pressure; LHV: Lower Heating Value; NOx: Nitric Oxide.

Experimental investigation on in-cylinder working process and thermal efficiency of ammonia/diesel low-carbon engine with pre-injection strategy

Ammonia, as a zero carbon and sustainable fuel, combined with traditional diesel fuel can provide a promising solution for reducing the engine environmental impact. However, ammonia/diesel dual-fuel (ADDF) engine has the significant drawback of low combustion efficiency and poor combustion stability at low loads, which seriously hinders its development. Therefore, this study explored the potential of pre-injection strategy in improving the performance of ADDF engine, comprehensively evaluating the effects of four pre-injection parameters (main injection timing (MIT), pre-injection timing (PIT), pre-injection quantity (PIQ), and diesel injection pressure (DIT)) on in-cylinder combustion process, incomplete combustion emissions, and energy efficiency. The results indicate that MIT has the most significant impact on combustion process. Advancing MIT can significantly increase in-cylinder combustion pressure and reduce CO, HC and unburned NH3 emissions. At MIT = -12 °CA ATDC, the highest brake thermal efficiency (BTE) of 32.3 % is obtained, while simultaneously generating high combustion noise. The advance of PIT has adverse effects on combustion stability. When PIT is advanced from −24 °CA ATDC to −36 °CA ATDC, COVIMEP increases from 2.61 % to 4.44 %, unburned NH3 emission increases by 23.5 %, and the BTE of ADDF engine decreases. Adjusting the PIQ and DIP can improve the reactivity distribution of fuel and reduce incomplete combustion emissions. However, the decrease in main injection quantity would increase the cycle fluctuation. At low loads, shortening the pre-main injection interval and increasing PIQ and DIP can enable the engine to achieve higher BTE while reducing pollutant emissions. This study elucidates in detail the influence of four pre-injection parameters on the operation characteristics of ADDF engine. It can offer insights and practical references for expanding the operating range of ammonia fuel engine.

Acoustic Design Parameter Change of a Pressurized Combustor Leading to Limit Cycle Oscillations

When aiming to cut down on the emission of nitric oxides by gas turbine engines, it is advantageous to have them operate at low combustion temperatures. This is achieved by lean premixed combustion. Although lean premixed combustion is a proven and promising technology, it is also very sensitive to thermoacoustic instabilities. These instabilities occur due to a coupling between the unsteady heat release rate of the flame and the acoustic field inside the combustion chamber. In this paper, this coupling is investigated in detail. Two acoustic design parameters of a swirl-stabilized pressurized preheated air (300 °C)/natural gas combustor are varied, and the occurrence of thermoacoustic limit cycle oscillations is explored. The sensitivity of the acoustic field as a function of combustion chamber length (0.9 m to 1.8 m) and reflection coefficient (0.7 and 0.9) at the exit of the combustor is investigated first using a hybrid numerical and analytical approach. ANSYS CFX is used for Unsteady Reynolds Averaged Navier-Stokes (URANS) numerical simulations, and a one-dimensional acoustic network model is used for the analytical investigation. Subsequently, the effects of a change in the reflection coefficient are validated on a pressurized combustor test rig at 125 kW and 1.5 bar. With the change in reflection coefficient, the combustor switched to limit cycle oscillation as predicted, and reached a sound pressure level of 150 dB.

Impulse generated from detonation waves in non-premixed and partially premixed reactants

Rotating detonation engines (RDEs) are the subject of research in the combustion community due to the prospects of enhanced thermal efficiency and power density when compared to current deflagrative-based aerospace combustors. Many current simulations presume premixed reactants and therefore miss the important characteristics of transient mixing, wave-induced mixing, and injector design/spacing that are known to play a pivotal role in the system performance. Very ambitious large eddy simulations are being conducted, but necessarily on a limited number of realistic and complex cases, thus limiting their utility in deriving fundamental understanding. For these reasons, a two dimensional parametric study was conducted to assess propagation of a detonation across an idealized array of mixing/injection sites, parametrically characterized by the width and axial mixing profile.Under such non-premixed conditions, discrete energy release and interdependence are observed. The discrete energy release sites frequently create pressures that exceed idealized Chapman-Jouguet (CJ) predictions based on perfect and uniform mixtures. The local higher pressure is shown to be caused by delayed heat release behind the shock, near constant pressure combustion, and additional compression due to the non-uniformities present. The resulting compression and the near constant pressure combustion are accompanied by time scale separation of exothermic and endothermic reactions due to the mixing efficiencies in the non/poorly-premixed cases. In contrast, the better mixed cases show that the detonation wave is sustained but unburnt fuel and oxidizer exist behind the main combustion wave and impulse performance suffers. Results show that for the conditions modeled there exists an optimal injector spacing to maximize the impulse produced and that discrete injection impulses can exceed that of the premixed systems. These somewhat counter-intuitive results imply that the detailed mixing evolution, provoked by the passage of the wave can lead to an extended heat release zone that elevates the pressure over a longer distance along the wavefront. These revelations provide potential for optimizing injector configurations for real non-premixed systems in order to exploit these physics.

Estimation of Piston Surface Temperature During Engine Transient Operation for Emissions Reduction

Abstract Piston surface temperature is an important factor in the reduction of harmful emissions in modern gasoline direct injection (GDI) engines. In transient operation, the piston surface temperature can change rapidly, increasing the risk of fuel puddling. The prediction of the piston surface temperature can provide the means to significantly improve multiple-pulse fuel injection control strategies through the avoidance of fuel puddling. It could also be used to intelligently control the piston cooling jet (PCJ), which is common in modern engines. Considerable research has been undertaken to identify generalized engine heat transfer correlations and to predict piston and cylinder wall surface temperatures during operation. Most of these correlations require in-cylinder combustion pressure as an input, as well as the identification of numerous model parameters. These requirements render such an approach impractical. In this study, the authors have developed a thermodynamic model of piston surface temperature based on the global energy balance (GEB) methodology, which includes the effect of PCJ activation. The advantages are a simple structure and no requirement for in-cylinder pressure data, and only limited experimental tests are needed for model parameter identification. Moreover, the proposed model works well during engine transient operation, with maximum average error of 6.68% during rapid transients. A detailed identification procedure is given. This and the model performance have been demonstrated using experimental piston crown surface temperature data from a prototype 1-liter 3-cylinder turbocharged GDI engine, operated in both engine steady-state and transient conditions with an oil jet used for piston cooling turned both on and off.

Experimental Investigation of Thermoacoustics and High-Frequency Combustion Dynamics with Band Stop Characteristics in a Pressurized Combustor

In combustor systems, thermoacoustic instabilities may occur and must be avoided for reliable operation. An acoustic network model can be used to predict the eigenfrequencies of the instabilities and the growth rate by incorporating the combustion dynamics with a flame transfer function (FTF). The FTF defines the interconnection between burner aerodynamics and the rate of combustion. In the current study, the method to measure the FTF in a pressurized combustor is explored. A siren unit, mounted in the fuel line, induced a fuel flow excitation of variable amplitude and high maximum frequency. This was performed here for pressurized conditions at 1.5 bar and 3 bar and at a thermal power of 125 kW and 250 kW. In addition to the experimental investigation, a 1-D acoustic network model approach is used. In the model, thermoviscous damping effects and reflection coefficients are incorporated. The model results compare well with experimental data, indicating that the proposed method to determine the FTF is reliable. In the approach, a combination of an FTF with a band stop approach and a network modeling approach was applied. The method provides a good match between experimentally observed behavior and an analytical approach and can be used for instability analysis.

Effect of initial pressure on hydrogen/propane/air flames in a closed duct

To investigate the flame propagation characteristics and chemical kinetics of premixed propane/hydrogen/air mixtures at elevated pressure, a series of experiments on propane/hydrogen/air mixtures with varying initial pressures (P0 = 100–300 kPa) and equivalence ratios (φ = 0.6–1.4) at a hydrogen fraction of 0.6 and an ambient temperature of 298 K were carried out in a closed duct with an aspect ratio of 15. The chemical kinetics of the elementary reaction were analyzed numerically. The results revealed that the combustion-induced rapid phase transition (cRPT) occurred in the premixed C3H8/H2/air flames. Both the combustion pressure and flame propagation velocity increase with initial pressure except at P0 = 300 kPa, where the flame propagation velocity decreases. Moreover, the linear dependence between the laminar burning velocity and peak mole fraction [H + O + OH]max was found by the effect of initial pressure on the peak mole fraction (H, O, OH). The explosion pressure Prea and the maximum rate of production of free radical H/O show excellent correlations. The maximum rate of pressure rise can be predicted by the maximum heat release rate (HHR). These results provide essential data on elevated-pressure duct accidents and have important implications for explosion prevention.

In-situ synthesis of MEMS compatible Al/Cu2HIO6/PVDF Metastable composites film with high combustion performance

To address the challenges related to significant pressure loss and weakened combustion performance of energetic materials when ignited on Micro-Electro-Mechanical Systems (MEMS), periodate-based MICs (Metastable Intermolecular Composites) have emerged as promising candidates due to their high energy density and combustion pressure. However, the integration of periodate-based MICs onto MEMS has not been effectively achieved thus far. Herein, we propose a simple, environmentally friendly, and cost-effective approach to fabricate a MEMS-compatible Al/Cu2HIO6/PVDF (polyvinylidene difluoride) energetic composite film. Our method involves utilizing a Cu(OH)2 array as a template and employing an in-situ and spin-coating process. The resulting Al/Cu2HIO6/PVDF film was characterized using various techniques including SEM, TEM, XRD, and XPS. These analyses reveal a tightly packed nano array morphology with a porous structure. DSC-TG analysis was conducted to investigate the thermal reaction of the Al/Cu2HIO6/PVDF composite film. The results demonstrate that the thermal reaction involved a complex multi-step process, with higher heat release (1121 J g-1), a faster reaction rate, and a lower initial reaction temperature (294.5 °C) compared to the Al/CuO/PVDF composite film. the reaction process of Al/Cu2HIO6/PVDF film was also been proposed by analyzing the products at different temperatures. combustion diagnostic tests were carried out to evaluate the combustion performance of the Al/Cu2HIO6/PVDF composite film. The results indicate that as CuO transformed into Cu2HIO6, the film exhibits a reduced ignition delay (8 ms) and combustion duration (50 ms), higher combustion temperature (3710 K), and stronger flame intensity (8630 a.u.).

Scramjet Intake Aerodynamic Studies Using Sharp Interface Immersed Boundary Method

In this present article, the use of a throttling device in the form of movable flap to study scramjet inlet unstart has been investigated numerically. The flap has been employed as an effort to simulate the rise in combustor pressure of the scramjet. Computational analysis for freestream Mach number and freestream pressure of and respectively, have been performed by a two-dimensional compressible CFD in-house Finite volume solver for perfect gas. Convective fluxes have been evaluated using AUSM scheme.Inviscidflow has been assumed for all the simulations. Particular point of interest in these simulations is the application of Immersed Boundary Method along the wall boundaries,enabling the use of structured grid for complex geometries. The results demarcate the starting condition of the inlet based on the flap throttling values. Comparative results in the form of Mach number and pressure contours are presented for different flap positions. The use of Immersed Boundary Method has been successfully displayed bysimulating a movable flap.

Fabrication of Al@AIH@PVDF metastable composite film with enhanced laser ignition ability and combustion performance

Laser ignition technology has garnered significant attention for energetic materials in recent years, offering advantages over traditional electrical initiation methods, notably in mitigating issues related to stray currents and electromagnetic interference. Moreover, it can facilitate multi-point synchronous ignition. However, the persistent challenges of high ignition thresholds and delays in energetic materials necessitate effective resolutions. In this study, we address these challenges by converting the inert Al2O3 layer on the surface of aluminum powder into the active compound Aluminum Iodate Hexahydrate ([Al(H2O)6](IO3)3(HIO3)2, AIH) to prepare an Al@AIH@PVDF energetic composite film (ECF) with the aim of reducing the laser ignition threshold and delay of Al@PVDF ECF. The Al@AIH@PVDF ECF was synthesized through a simple wet chemistry method and a rapid evaporation process suing a simple, environmental-friendly, and cost-effective way. Differential scanning calorimetry-thermogravimetric analysis (DSC-TG) results demonstrate a lower exothermic reaction temperature (161 °C) and higher heat release (2900 J g−1) for Al@AIH@PVDF ECF. Laser ignition tests reveal a reduced laser ignition delay (11 ms) and threshold (1.59 J cm−2) for Al@AIH@PVDF ECF. Combustion experiments showcase elevated combustion flame temperature (3090 K), burning rate (4.11 cm s−1), and smaller condensed combustion products, while effectively igniting CL-20. Pressure tests indicate higher maximum combustion pressure (3.24 MPa) and pressure rise rate (4.05 GPa s−1) for Al@AIH@PVDF ECF. Finally, the reaction process and mechanism of Al@AIH@PVDF ECF was also investigated and proposed.

Combustion performance and emission characteristics of aloevera diesel-emulsified fuel in a DI diesel engine.

Nowadays, mankind is very particular about the usage of energy in the most effective manner by keeping the view of less adulterating the atmosphere, which are the key aspects of many scientists all around the world. In this particular study, the aloevera diesel has been chosen as the primary fuel, and studies have been conducted on emission pollutant characteristics by choosing an appropriate diesel engine. Furthermore, stable emulsions have been produced by using aloevera, and the same was mixed with diesel at the ratio of 5% and 10% as the compound. Moreover, span 80 and tween 80 are used as the surfactant with an HLB balance of 9.95. Similarly, the emulsions are prepared with the help of a mechanical stirrer for exact duration of 30min. In order to carry out the experimental investigation process, a single-cylinder diesel engine was used with a data acquisition system. The entire analyses are carried out with two sets of methods such as no load and full load. The performance and combustion characteristics such as heat release, combustion pressure, thermal efficiency (B5 - 6.303%↑, B10 - 3.789%↑), and specific fuel consumption of the brake (B5 - 4.2%↑, B10 - 5%↑) were measured. Likewise, emission parameters such as CO (B5 - 0.02%↓, B10 - 0.04%↓), HC (B5 - 1 PPM↓, B10 - 5 PPM↓), NOx (B5 - 20 PPM↓, B10 - 89 PPM↓), and CO2 (B5 - 0.3%↑, B10 - 0.4%↑) are measured by using AVL Di-gas analyzer. It was noticed that increased peak cylinder pressure and greater heat release rate were on account of a longer ignition delay period. Additionally, an increase in engine performance and the corresponding reduction in exhaust emission have also been observed upon using aloevera-emulsified diesel fuel.

Performance and Emission Optimisation of an Ammonia/Hydrogen Fuelled Linear Joule Engine Generator

This paper presents a Linear Joule Engine Generator (LJEG) powered by ammonia and hydrogen co-combustion to tackle decarbonisation in the electrification of transport propulsion systems. A dynamic model of the LJEG, which integrates mechanics, thermodynamics, and electromagnetics sub-models, as well as detailed combustion chemistry analysis for emissions, is presented. The dynamic model is integrated and validated, and the LJEG performance is optimised for improved performance and reduced emissions. At optimal conditions, the engine could generate 1.96 kWe at a thermal efficiency of 34.3% and an electrical efficiency of 91%. It is found that the electromagnetic force of the linear alternator and heat addition from the external combustor and engine valve timing have the most significant influences on performance, whereas the piston stroke has a lesser impact. The impacts of hydrogen ratio, oxygen concentration, inlet pressure, and equivalence ratio of ammonia-air on nitric oxide (NO) formation and reduction are revealed using a detailed chemical kinetic analysis. Results indicated that rich combustion and elevated pressure are beneficial for NO reduction. The rate of production analysis indicates that the equivalence ratio significantly changes the relative contribution among the critical NO formation and reduction reaction pathways.

Tuning combustion and energy in hydroxylammonium nitrate (HAN)-based electrically controlled solid propellant

Solid propellants have been widely applied due to its high energy, rapid reaction, easy storage and convenient equipment. However, the further development of solid propellants has been hindered by the challenges associated with controlling their combustion process. In this research, we presented an electrically controlled solid propellant (ECSP), and its burning rate could be continuously adjusted with voltage. We investigated thermal decomposition behavior and gaseous products of ECSP using thermogravimetry–differential scanning calorimetry-mass spectrometry (TG-DSC-MS). The solid products were analyzed through energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Based on the thermal decomposition behavior, gaseous products, and solid products, it was found that the thermal decomposition process could be divided into two stages: decomposition of ammonium nitrate (AN) and interactions between hydroxylamine nitrate (HAN) and other substances. The electrochemical impedance spectroscopy (EIS) experiments revealed that the electrical conductivity of ECSP increased with the pressure. Significantly, the peak combustion pressure of propellant increased by the rise of voltage from 3.17 MPa (150 V) to 5 MPa (250 V) in closed bomb. In addition, electricity reinforced the burning rate and powder force of propellant. Additionally, the electricity simultaneously affects electric and thermal decomposition processes. Electricity is used to control the burning rate and the total energy produced by propellant combustion. The characteristics of controllable energy has the potential to achieve controllable range of weapons, providing a new direction for development of smart weapons.

Dynamic laser ignition characteristics of solid fuel and oxygen for hybrid rocket system

The transient laser ignition process in a slab burner that is similar to hybrid rocket motors is investigated in this study. The coupling characteristics between solid fuel properties, pyrolysis rate, and laser power were analysed. The results show that the laser ignition process can be divided into four stages: preheating, pyrolysis, ignition, and combustion, with the preheating and pyrolysis stages primarily controlled by the solid heating rate and the mixing characteristics in the fuel-rich combustion zone. Meanwhile, the ignition and combustion stages were characterized by ignition kernel growth and flame front propagation. The ignition delay time and the establishment of steady-state combustion were significantly affected by the ignition energy and fuel properties, i.e., The ignition delay time increases exponentially with decreasing laser energy. An increase in oxidizer flow flux reduces the demand for mixing during ignition, but the corresponding increase in combustion pressure poses challenges to the ignition process. A two-dimensional transient numerical model was established based on optical-thermal coupling theory to further understand the dynamic pyrolysis process of solid fuel particles. The model was validated through fire experiments under different laser ignition energy conditions. The results indicate that the deviation of the maximum penetration depth and ignition delay time between the experiment and the simulation is within 7 %.

The Influence of Ozone on the Flame Propagation Behavior of n-Heptane/air and i-Octane/air Premixed Flame in an Engine-Relevant Environment

ABSTRACT The promotional effect of ozone on lean premixed spherical flame propagation in an engine-relevant, high-temperature, high-pressure environment was investigated using an optically accessible rapid compression and expansion machine (RCEM). The laminar burning velocity, burned gas Markstein length, and initial flame development time based on mass fraction burned (MFB), were examined for n-heptane/air and i-octane/air premixture (φ = 0.55) with 15 [ppm] ozone, through self-emission observation of a propagating flame with a high-speed camera and combustion pressure analysis. The results showed that ozone reduced the initial flame development time and increased the laminar burning velocity for n-heptane/air premixture under temperature conditions in which the low-temperature oxidation (LTO) reaction was more clearly pronounced; but ozone did not enhance either the initial flame development or the laminar burning velocity in the case of i-octane/air premixture, where the LTO reaction was weak owing to the fuel molecular structure, even under the same temperature conditions. These results suggest that the enhancement of the LTO reaction by ozone, and the subsequent generation of thermal energy and CO radicals through an H2O2 loop reaction in the pre-flame region, were responsible for the increase in the laminar burning velocity. Furthermore, ozone increased the burned gas Markstein length, flame thickness, and Zeldovich number of the n-heptane/air mixture under the temperature conditions in which the laminar burning velocity was enhanced by ozone. This suggests that the chemical reaction in the reaction zone was more active in response to the increase in flame temperature.

Health monitoring of in-cylinder sensors and fuel injectors using an external accelerometer

This paper focuses on the development of a methodology to monitor the health of an engine by detecting any failures in the fuel injectors or in-cylinder pressure sensors using an accelerometer that is non-intrusively mounted on the engine block. A multi-cylinder engine with each cylinder having its own pressure sensor and injector is considered. First, a model relating the combustion component of the measured acceleration signal to the combustion component of in-cylinder pressure is proposed. Then, gains of the model are tuned to reduce the cycle-to-cycle estimation error by analyzing cycle-to-cycle variations with respect to the combustion pressure peak and engine vibration peak. Using the developed model, cylinder combustion pressures are estimated from engine vibration signals with small cycle-to-cycle estimation errors. Subsequently, a health monitoring system that can detect faults in pressure sensors, fuel injectors, and the accelerometers is proposed based on residues obtained from the difference between estimated combustion pressure and measured pressure signals. The source of the failed component can be identified uniquely by analyzing the pattern of residues. The proposed combustion pressure estimation algorithms are validated by extensive evaluation with experimental data obtained by operating a four-cylinder compression-ignition direct-injection engine with a range of experimental data. Finally, the developed health monitoring system is evaluated with various failure scenarios involving faults in the in-cylinder pressure sensor, fuel injector, and accelerometer.

Experimental study on the combustion and pressure drop characteristics of a pintle injector for LOX/kerosene rocket engine

Pintle injectors have attracted much attention in recent years for their excellent throttling and combustion performance. However, the combustion characteristics of cryogenic propellant on pintle injectors with varying operating conditions remain unclear. A LOX/kerosene throttleable rocket engine with a fuel-centered liquid-liquid pintle injector was designed and its pressure drop and combustion characteristics were tested. The pintle engine achieved stable combustion with the total flow rate and oxygen-fuel mixture ratio varying from 59 to 559 g/s and from 0.73 to 1.02. A calculation model for the gas ratio in the LOX channel of the pintle injector was established. The deviation of measurements from the calculated values did not exceed ±10%. The vaporization of LOX from the pintle injector in the hot test was calculated and the positive correlation between gas ratio and combustion efficiency was analyzed. For the phenomenon of low-frequency oscillation of pressure in the hot tests, the source and development process of the oscillation were studied by FFT. The primary frequency and amplitude of low-frequency oscillation had been discovered to exhibit a positive correlation with the gas ratio. Low pressure drop of injection was the main cause of low-frequency oscillation. The strong vaporization of LOX under low operating conditions made the combustion efficiency remain in a high range even if low-frequency oscillation was observed. This work can provide a reference for the design of pintle injectors for cryogenic liquid rocket engines that can be deeply throttled.

Review on thermal-science fundamental research of pressurized oxy-fuel combustion technology

Review on thermal-science fundamental research of pressurized oxy-fuel combustion technology