Pulse Jet Engines Research Articles

Computational Approach in Sizing of Pulsejet Engine

<p>Research in pulsejet has intensified recently due to its design simplicity that can be developed into efficient small scale propulsive units for new applications such as UAVs and Unmanned Combat Vehicles (UCAV). A major obstacle for its development is low efficiency of the engine. The objective of this research is to investigate the possibility of using pulsejet in certain applications where the pulsejet can trade its low efficiency with low cost, simple design, and light weight. Numerical analysis is used for analysing the pulsejet engine design. The main results drawn from this research is in increasing efficiency and improving performance of engine by improving size of engine, especially diameter of combustion chamber. The computed results show good resemblance with published data.</p>

Numerical simulation of a hydrocarbon fuelled valveless pulsejet

Jet propulsion technology has been limited to being identified largely with turbojets and turbo-machinery driven jet engines. Of late there has been a renewed interest in pulsejet technology and it has once again caught the imagination of academia. The specific characteristics of the pulsejet, such as easy scalability, absence of moving parts, reduced combustion temperatures; lower NOX formation and the like make it possess varied capabilities for use in the field of jet propulsion and the most viable option for small-scale jet propulsion.In the current work, a numerical analysis encompassing feasibility and validation of a valveless pulsejet engine was attempted using CD-adapco׳s STAR-CCM+ CFD package. Due to lack of comprehensive established mathematical laws to govern the working of a pulsejet, most experimental work being performed is done by trial and error. This necessitates in-depth computational studies in order to shed more light on the understanding of valveless pulsejets. The results have been encouraging and in agreement with observed experimental conclusions such as, i) changes in dimensions affect the working of a pulsejet, ii) presence of a flare enhances the working of a pulsejet, and the close agreement in the frequency of operation. Through continuous study, an optimum initial condition was achieved which enabled the pulsejet to begin operation even before 0.05s, thereby greatly reducing computational costs if a higher time-scale were to be used.

Pulse Jet Orchard Heater System Development: Part I. Design, Construction, and Optimization

The objective of this six-year project was to develop a more efficient and effective supplemental orchard field heater technology. In addition to being low-cost and mobile, these devices should be useable with or without wind machines, reduce labor requirements, and greatly reduce air pollutants compared to conventional orchard heating systems. The new generation orchard heaters that were developed in this process are portable, auto-regulating, horizontal pulse jet engines (combustors) with no moving parts. These devices utilize air ejector technology to reduce the temperature of the high-velocity combustion stream by thoroughly mixing it with the surrounding ambient (cold) air, producing a net effective temperature increase of only 2°C to 5°C above ambient. Buoyant forces of warm air are therefore small, and fewer heaters would be needed. The design achieved pressure oscillations that were free of combustion instabilities, and amplitudes were maximized for high exhaust jet velocities for deep hot jet penetration and mixing into the surrounding cold air. The overall size and weight of the heater system were minimized while maintaining optimum operation. Finally, anti-phase operation of paired heaters for noise level reduction from 130 dB to near 75 dB was achieved by implementing optimized silencing plenums at the inlet and exhaust of the paired heaters.

Pulse Jet Orchard Heater System Development: Part II. System Scaling and Application

This article reports the results of a six-year project in which an efficient and effective supplemental orchard field heater system was successfully developed. In addition to being low-cost and mobile, the criteria met by this system design included: (1) usage with or without wind machines or as stand-alone units, (2) reduced labor requirements, and (3) reduced air pollutants compared to conventional supplemental, fossil fuel combustion orchard heating systems. The resulting new generation heaters were portable, auto-regulating, horizontal pulse jet engines (combustors) with no moving parts. Scaling criteria were formulated and utilized for fabrication of various sizes of portable horizontal pulse jet engines optimized for stable operation. Scale-up parameters for multiple sizes of these combustor systems for agricultural heating and frost protection purposes were both theoretically and qualitatively described. Theoretical and empirical approaches resulted in similarity parameters that played an important role in the scale-up for field applications. The scaled and optimized heater prototypes were constructed and field tested. Experimental results confirmed the applicability of using both gaseous and liquid propane as fuel supplies. Detailed field testing showed that mixing of warm air by the high-velocity exhaust stream into cold air (0 to 4 m height) was quite effective in reducing buoyant heat losses. Pulse jet heater prototypes were also tested under orchard conditions and found to circumvent the many disadvantages of conventional oil and liquid propane (LP) gas orchard heating systems, especially when used in combination with wind machines.

A New Acoustic Model for Valveless Pulsejets and Its Application to Optimization Thrust

Due to its simplicity, the valveless pulsejet may be an ideal low cost propulsion system. In this paper, a new acoustic model is described, which can accurately predict the operating frequency of a valveless pulsejet. Experimental and computational methods were used to investigate how the inlet and exhaust area and the freestream velocity affect the overall performance of a 50cm pulsejet. Pressure and temperature were measured at several axial locations for different fuel flow rates and different geometries. Computer simulations were performed for exactly the same geometries and fuel flow rates using a commercial CFD package (CFX) to develop further understanding of the factors that affect the performance of a valveless pulsejet. An acoustic model was developed to predict the frequency of these valveless pulsejets. The new model treats the valveless pulsejet engine as a combination of a Helmholtz resonator and a wave tube. This new model was shown to accurately predict geometries for maximum thrust. The model was further extended to account for the effect of freestream velocity. Evidence is provided that valveless pulsejet generates the highest thrust when the inherent inlet frequency matches the inherent exhaust frequency.

A mathematical model of vibration combustion in a tube with sudden cross-section change

The theoretical study of vibration combustion using a model of the pulsejet engine was carried out. The frequencies and amplitudes of gas vibrations that were calculated by the energy method are well agreed with experimental data.

Numerical simulation of nonstationary gasodynamic processes in a pulsejet engine

A method of numerical simulation of nonstationary gasodynamic processes in a pulsejet engine is proposed. The method makes it possible to provide a rather high precision for computational grids both with small and large cells. The calculation results showed a good agreement with the experimental data.

Gas-flow fluctuation velocity within exhaust tube of pulse-jet engine

Gas-flow fluctuation velocity within exhaust tube of pulse-jet engine

Simulation of a working process in the pulsejet engine with an aerodynamic valve on the basis of the thermodynamic cycle analysis

A physical and a mathematical model of a working process in the pulsejet engine based on the analysis of the thermodynamic cycle are proposed. The process of self-sustained periodic combustion is connected with special features of elementary processes comprising the cycle, influencing the engine operation and depending on its design parameters. The calculation method is based on the use of fundamental laws of conservation and basic equations of gas dynamics

Effect of exit geometry of tail pipe on the performance of pulse jet engines

In this paper, the effect of geometries of tube open end on the shock, compression and expansion waves propagating in the tube was investigated numerically and experimentally. One of them is a conventional straight shock tube with an open end. The other has a divergent tail tube at the exit. Applying a divergent tail tube (flare tube) to an open end shock tube, the period of one-cycle process could be shortened and the pressure behind the expansion wave produced at the exit of the shock tube could be lowered much more below the atmospheric pressure than that produced in the straight tube. The results suggested that the intake air into the engine was significantly increased by applying a flare tube instead of a straight tube.

Interaction of masses in the operating process of pulse jet engines as a means of increasing their thrust efficiency

Experimental and calculational-theoretical studies have been made of the operating process of pulse jet engines. With certain combinations of parameters of the operating pulsations, the interaction of cyclic gas masses among themselves or with the external medium (with and without the ejector channel alike) is possible, which provides an increase in the thrust efficiency of the engine.

Experimental study of twin pulse jet engines for power plant application

The total efficiency of power plants depends on the energy conversion in a combustor and a turbine. Considerably higher energy transfer rates can be obtained from a pulsed combustion, but unsteady flow of a single jet combustor reduces the turbine efficiency. Therefore, two pulse combustors were set in parallel and connected to a settling chamber that supplies a flow with constant pressure to the turbine. The aim of investigations presented here is a demonstration of technical feasibility for industrial applications and to show the benefits obtained from the pulse combustors.

Experimental study of twin pulse jet engines

The total efficiency of power plants depends on energy conversion in a combustor and a turbine. Considerably higher energy transfer rates can be obtained from a pulsed combustion although unsteady flow of a single jet combustor reduces the turbine efficiency. Therefore, two pulse combustors were set in parallel and connected to a settling chamber that supplies a flow with constant pressure to the turbine. The aim of investigations presented here is a demonstration of technical feasibility for industrial applications and to show the benefits obtained from the pulse combustors.

Propulsion System for Hypersonic Space Planes

Because of its simple construction and low weight, combined rocket, ramjet, pulse-jet engines, or detonation enginesinsteadofturbojets,weretakenintoconsiderationaspropulsionforhypersonicaircraft.Combinedpropulsion requires an active control system to change the propulsion operation mode and to sustain the high-efe cient pulse combustion. Therefore, the transient behavior of the combustor is investigated to show the benee ts that can be gained, especially from a pulse combustor with active control. Several experiments were performed to survey system performance and to e nd suitable control parameters and strategies. Propulsion installation, including thrust augmentation, is considered to dee ne the tasks of the combustor controller. Nomenclature A = cross section b = fuel consumption c = sound velocity D = pipe diameter F = thrust f = frequency H = net calorie c value L = tail pipe length M = Mach number C m = mass e ow n = rotational speed P = pressure Re = Reynolds number T = temperature t = time u = velocity X, Y = coordinates a = angle of attack D P = pressure amplitude g = efeciency j = ratio of specie c heats q = density Subscripts and Superscripts

Studies on Pulse Jet Engine by Wind Tunnel Testing

Simple design and efficiency make pulse jet engines attractive for aeronautical short‐term operation applications. An active control system extends the operating range and reduces the fuel consumption considerably so that this old technology might gain a new interest. The results on wind tunnel experiments have been reported together with the impact of combustion mode (pulse or steady) on system performance.

A Statistical Investigation of Ignition in a Fuel Spray Using a Shock Tube.

In order to determine the general aspect of the spontaneous ignition in a fuel spray injected in compressed air at high temperature, which takes place usually in diesel and pulse jet engines, an experimental method using a shock tube is developed. A shock wave driven by high-pressure He gas propagates in the air in the low-pressure tube and reflects at a shock tube end. Through application of the pressure of the shock wave at reflection, n-octane fuel is injected into the air behind reflected shock waves in the shock tube. The fuel injection space is optically separated into 5 regions in the vertical direction, and the induction period of spontaneous ignition in each region is separately observed. As the induction period fluctuates markedly, the measured results are treated statistically and analyzed on the basis of the stochastic ignition theory.

A Statistical Investigation of Ignition in a Fuel Spray using a Shock Tube.

In order to obtain a general aspect of the spontaneous ignition in a fuel spray injected in compressed air at high temperature, which takes place usually in diesel and pulse jet engines, an experimental method using a shock tube is developed. A shock wave driven by high-pressure He gas propagates in the air in the low-pressure tube and reflects at a shock tube end. Through application of the pressure of the shock wave at reflection, n-octane fuel is injected into the air behind reflected shock waves in the shock tube. The fuel injection space is optically separated into 5 regions in the vertical direction, and the induction period of spontaneous ignition in each region is separately observed. As the induction period fluctuates markedly, the measured results are treated statistically and analyzed on the basis of the stochastic ignition theory.

A SPECTROPHOTOMETRIC DETERMINATION OF EXHAUST GAS TEMPERATURES IN THE PULSE-JET ENGINE

This paper describes a spectrophotometric method whereby instantaneous values of a variable flame temperature, in the particular case of nonluminous flames, may be determined and continuously recorded.This new technique, which depends upon the establishment of monochromatic black-body radiation conditions in the flame for a small region in the visible spectrum, involves the continuous measurement of radiation intensity in the above region, the intensity being, thereafter, correlated with the temperature of the flame.The problem of temperature measurement in the general case of nonluminous flames (flames which do not contain an appreciable amount of free carbon in the form of soot) is considered and a brief review of previous techniques employed for this purpose over the past 50 years is given. The basic theory and preliminary experimental justification of the present method are discussed.A description of the apparatus and the experimental arrangement used by the author in a specific application of the present method in the determination of the time variation of temperature in the exhaust flame of a pulse-jet engine is given. This includes details of a special type of spectrophotometer which employs a multiplier photocell as the radiation detecting and measuring element and, also, a "black-body" cavity constructed as a standard radiation source for the calibration of the former instrument. An original technique used to investigate the emissivity of flames colored by alkali metal vapors is described and its application to the present problem shown.Finally, the measurable temperature range of the present apparatus is considered together with the inherent limitations of the new method.

A Frequency Modulation Pressure Recording System

A simple frequency-modulated pressure gauge employing a variable capacity pick-up element has been devised to measure the oscillating pressures of burning gases. It has been used to measure pressures in pulse jet engines ranging from −5 to +60 p.s.i. gauge, under conditions where the gas temperatures ranged from approximately 300°K to 2450°K and the gauge mount vibrated with an amplitude of approximately 0.125 inch. The fundamental frequencies of temperature variation, pressure variation and mechanical vibration were 40 cycles and 220 cycles per second. Under these conditions the pressure response is essentially linear from 0 to 5500 cycles per second.