Development of a Reed Valve Model for Engine Simulations for Two-Stroke Engines

The Microwave Rocket is a candidate for a low cost launcher system. Pulsed plasma generated by a high power millimeter wave beam drives a blast wave, and a vehicle acquires impulsive thrust by exhausting the blast wave. The thrust generation process of the Microwave Rocket is similar to a pulse detonation engine. In order to enhance the performance of its air refreshment, the air‐breathing mechanism using reed valves is under development. Ambient air is taken to the thruster through reed valves. Reed valves are closed while the inside pressure is high enough. After the time when the shock wave exhausts at the open end, an expansion wave is driven and propagates to the thrust‐wall. The reed valve is opened by the negative gauge pressure induced by the expansion wave and its reflection wave. In these processes, the pressure oscillation is important parameter. In this paper, the pressure oscillation in the thruster was calculated by CFD combined with the flux through from reed valves, which is estimated analytically. As a result, the air‐breathing performance is evaluated using Partial Filling Rate (PFR), the ratio of thruster length to diameter L/D, and ratio of opening area of reed valves to superficial area α. An engine cycle and predicted thrust was explained.

<div class="htmlview paragraph"> </div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">A computer simulation of a high performance two-stroke engine has been validated by a transient test method. The simulation included unsteady gas dynamics, together with detailed mechanical models for the reed valve, etc. The combustion model used Vibe coefficients derived directly from measured cylinder pressures. Cylinder scavenging characteristics which were measured on The Queen's University of Belfast (QUB) single-cycle rig were also incorporated in the simulation.</div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">Validation of the model involved use of an inertial dynamometer and data acquisition system which has been developed at QUB. This dynamometer incorporates a flywheel which is directly coupled to the engine. During a test, the engine is accelerated, and the torque and power are calculated from the flywheel speed characteristics. Further, at pre-determined engine speed intervals, the cylinder and exhaust pressures may be recorded. This testing system provided a convenient and rapid experimental method to acquire data.</div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">Measurement of power, pressures and temperatures during transient testing are discussed. Also presented are methods which reduce the errors arising from the slow response of thermocouples. The measured results are compared with the computer predictions for power and exhaust pressure. Excellent correlation was achieved.</div> <div class="htmlview paragraph"> </div>

<div class="section abstract"><div class="htmlview paragraph">Air Supply Unit (ASU) serves as the pneumatic source for the air suspension system in the passenger car segment. The ASU is an electrically driven oil-free compressor with integrated air dryer to deliver dry air to the suspension system. Solenoid valve, Height Sensor and ECU adjusts the pressure in bellow based on the vehicle load condition. During the lab test, pressure was not building up in the compressor due to delivery valve failure. The type of valve in asu is reed valve type, it is mostly used in the micro compressors due to its low cost, simple structure and light weight configuration. The reed movement is based on the pressure difference between the inlet and the compression chamber. Failure analysis is carried out based on the finite element analysis to identify the root cause, the root cause identified is optimized to prevent the failure. An accelerated test condition is arrived based on the FEA and a tailored series of accelerated tests are carried out to reproduce the failure. The correlation between the test results and the FEA was found satisfactory. The significant factors that are responsible for the failure are identified with their respective control measures. This paper describes the reed valve failure simulation using finite element method and accelerated testing.</div></div>

<div class="htmlview paragraph">Several studies are currently dealing with the so-called ‘new generation two-stroke engines’. In nearly all these, charge control by means of fuel injection has been proposed to overcome the well-known problems of fuel and lube-oil consumption, and the probably unacceptable level of pollutant emissions. Direct injection, in particular, seems to guarantee the best results as it allows to avoid the short-circuiting of the fuel to the exhaust.</div> <div class="htmlview paragraph">The direct-injection systems proposed in recent times do not seem to be widely applicable especially to small two-stroke engines as they introduce considerably complicated and consequently high-cost systems.</div> <div class="htmlview paragraph">A new direct injection system, based on the hydraulic phenomenon commonly known as “water hammer”, has been proposed by the authors as a reliable means of achieving high injection pressures while maintaining the simple manufacturing and low-cost characteristics of two-stroke engines. Though ideal for small two-stroke engines this concept appears suitable also for every other kind of spark-ignited engine.</div> <div class="htmlview paragraph">The system, equipped with a low-pressure fuel pump, provides high injection pressure values thanks to the conversion of the kinetic energy of the fluid into a local pressure rise which takes place when the fuel flow is suddenly halted by an automatic valve.</div>

<div class="htmlview paragraph">JUST YESTERDAY, simulation tackled the issues of digital technology in a new generation of aircraft, but here we face another quantum leap as we look beyond the Boeing 757/767 model airplanes. The engineering simulator has evolved, over a period of 25 years, from a relatively modest beginning, to a sophisticated design tool essential to the development of new airplanes and weapons systems. The decisions involved in the management of simulation facilities has also evolved from choosing a modest “take-what-you-can-get” product line, to picking from warehouses full of “goodies,” all of which have their associated payoffs.</div> <div class="htmlview paragraph">As a background, the authors will attempt to outline from personal experience and long-term history with engineering simulation, the steps that were taken to reach the present level of sophistication in engineering simulators at Boeing. Engineering flight simulators have assumed an increasingly crucial role in the development and testing of new product lines in the aviation industry. Significant flight operational cost savings have resulted from the new generation of digital systems, promoting airline fleet modernization. Both part-task and fully instrumented man-in-the-loop aircraft simulators are being used extensively for the development and integration testing of these new systems. Simulation has proven to be a high payoff tool with increasing recognition from a competitive airline industry. In other words, simulation has “come of age.”</div> <div class="htmlview paragraph">From a present day technology base, we will attempt to look down the tunnel of the future and consider the demands of simulation for 1990 and beyond. An ever-increasing growth in computing requirements arises from the increasing sophistication of new airplane hardware and airborne software, and from a user community which demands ever-increasing fidelity. More models of software need to be incorporated into simulations; more and better data is being made available, all leading to more detailed simulations than ever before. In addition, the user community keeps expanding, which often leads to developing simulations never before attempted. All of this requires management to re-evaluate computing structure, configuration, and implementation into a mini, micro, multi, and/or concurrent processing world.</div> <div class="htmlview paragraph">The arrival of the engineering workstation poses yet another challenge as many of the exclusive functions of the simulation programmer become accessible to the design engineer. This means developing adequate help systems, friendly user interface, and workstation integration into the real-time network. Artificial intelligence technology holds some promise for human interface issues, but systems available today are not sufficient to meet the needs. Last but not least, the demands of the future involve a global re-education of simulation software personnel toward Ada<span class="xref">*</span>, structured methodology, and “embedded” designs. Experience in the most prevalent simulation languages does not easily lend itself to this re-education process.</div> <div class="htmlview paragraph">Engineering flight simulation - it spells out a revolution of change, technology forefronts of the future, and exciting challenges to those involved.</div>

<div class="section abstract"><div class="htmlview paragraph">Emission reduction and efficiency increase of two-stroke marine diesel engine depends on fuel injection, which affects in-cylinder combustion. This paper presents injection strategies varied results from simulation based on AVL BOOST and the experimental results and its validity was confirmed by actual measurements in a two-stroke engine during shop testing, which reveals the affect on performance and emission, as well as the corresponding concept analysis. This simulation enabled a more thorough investigation into engine performance features. In particular it provided a detailed examination of how changes in injection strategies impacted the combustion and ultimately engine performance. These results are summarized and based on these results, optimal injection strategies settings are suggested for balancing engine performance and NOx emissions.</div></div>

<div class="htmlview paragraph">Controlled Auto-Ignition (CAI) combustion, also known as HCCI or PCCI, has recently emerged as a viable alternative combustion process to the conventional spark ignition (SI) or compression ignition (CI) process for internal combustion (IC) engines, owing to its potential for high efficiency and extremely low emissions. One of the most effective and practical means of achieving CAI combustion in an engine is to retain or recycle the burnt gases. In order to understand better the effects of recycled burnt gases on CAI combustion, detailed analytical and experimental studies have been carried out. The analytical studies were performed using an engine simulation model with detailed chemical kinetics.</div> <div class="htmlview paragraph">The five effects of the recycled burned gases studied include:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"><span class="li-label">(1.)</span><div class="htmlview paragraph">Charge heating effect: higher intake charge temperature due to hot burned gases;</div></li> <li class="list-item"><span class="li-label">(2.)</span><div class="htmlview paragraph">Dilution effect: the reduction of oxygen due to the presence of the burned gases;</div></li> <li class="list-item"><span class="li-label">(3.)</span><div class="htmlview paragraph">Heat capacity effect: due to higher specific heat capacity of burned gases;</div></li> <li class="list-item"><span class="li-label">(4.)</span><div class="htmlview paragraph">Chemical effect: chemical reactions involving CO<sub>2</sub> and H<sub>2</sub>O in the burned gases</div></li> <li class="list-item"><span class="li-label">(5.)</span><div class="htmlview paragraph">Stratification effect: recycled burned gases are stratified from the fuel/air mixture.</div></li> </ol> </div> <div class="htmlview paragraph">And the main conclusions are:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"><span class="li-label">(1.)</span><div class="htmlview paragraph">The charge heating effect is mainly responsible for the advanced AI timing due to hot burned gases. It increases the heat release rate and shortens the combustion duration.</div></li> <li class="list-item"><span class="li-label">(2.)</span><div class="htmlview paragraph">The dilution effect does not affect AI timing, but it extends combustion duration. Its slows down the heat release rate only when large amount of burned gases is present.</div></li> <li class="list-item"><span class="li-label">(3.)</span><div class="htmlview paragraph">The heat capacity effect is mainly responsible for the reduction in the heat release rate, and it has a similar effect to extend the combustion duration as the dilution effect.</div></li> <li class="list-item"><span class="li-label">(4.)</span><div class="htmlview paragraph">The chemical effect does not affect AI timing and heat release rate. It reduces the combustion duration slightly at high concentrations of burned gases.</div></li> <li class="list-item"><span class="li-label">(5.)</span><div class="htmlview paragraph">The stratified burned gases facilitate the CAI combustion due to the presence of higher temperature region at the boundary between of the hot burned gases and combustible charge.</div></li> </ol> </div>

<div class="htmlview paragraph">Recently, emission regulations formerly concentrated on the acknowledged major polluters, such as motor vehicle engine, have been extended to the smaller engines.</div> <div class="htmlview paragraph">This forced the two-stroke engines manufacturers to search for environmentally cleaner solutions. In this respect the most promising technology seems to be the adoption of direct-injection and the challenge is not to complicate excessively a power system which has in simplicity and low cost its best advantages.</div> <div class="htmlview paragraph">The paper reports on a two-stroke gasoline direct-injection engine prototype which even if equipped with a low-pressure fuel pump, provides high injection pressure values thanks to a Water-Hammer effect.</div> <div class="htmlview paragraph">The engine is a two-cylinders-water-cooled type and its design follows previous experiences on single-cylinder engines prototype.</div> <div class="htmlview paragraph">Once described the basic working principles of the proposed concept the engine realization phases and its running results on a test bed are presented.</div>

<div class="htmlview paragraph">Aluminum cylinder heads have been widely used on automobiles during the past fifteen years to increase the efficiency of engine operation. The great majority have given satisfactory service during many years of use and high mileages. In 1938 their use was greatly curtailed because of competitive costs. The competitive situation now prevailing favors the re-adoption of aluminum cylinder heads. Because of this, it is fortunate that the two problems formerly associated with the use of aluminum cylinder heads have been solved. One was difficult removal resulting from corrosion at the stud clearances. Tests have shown that this can be prevented easily by the use of cap screws, larger stud clearances, or stud coating compounds.</div> <div class="htmlview paragraph">The other problem was corrosion at the coolant inlet ports. The causes and means of prevention of this difficulty have been determined recently by means of road tests of seventeen automobiles, and cyclic tests of V-8 engines with divided radiators. It was learned that the corrosion can be prevented by simple methods which can be applied by the engine manufacturer at little or no added cost. The corrosion was found to result primarily from the galvanic couple formed with the iron cylinder block. Corrosion did not occur in road tests of engines having aluminum blocks as well as aluminum cylinder heads.</div> <div class="htmlview paragraph">One of the major factors affecting the rate of galvanic attack is the electrode potential of the cylinder head alloy. To achieve the low potential desired, the alloy should contain an adequate concentration of copper, and no more than a few tenths of a percent of zinc. Also, the alloy should be in the as-cast or solution heat-treated condition to retain sufficient copper in solid solution.</div> <div class="htmlview paragraph">Another effective means of reducing port corrosion was found to be the use of a protective design of cylinder head gasket which covered the port shoulders of the cylinder head and preferably extended into the ports. Such gaskets protect the shoulders against erosion and lengthen the paths of the galvanic currents.</div> <div class="htmlview paragraph">Proprietary alcohol and ethylene glycol antifreezes, and inhibitors used to prevent rusting of the iron cylinder block, were found to be important accelerators of port corrosion, particularly when mixed with water containing several hundred parts per million of chloride. These conclusions are contrary to those previously drawn from continuous engine tests before the development of cyclic testing. In the recent cyclic and road tests, the high chloride water when tested alone caused practically no corrosion. Also another municipal water high in chloride, sulphate, alkalinity, and copper, caused no appreciable corrosion. Straight ethylene glycol and methanol were less corrosive than the proprietary products, which contain inhibitors of iron corrosion. The amount of dilution of alcohol and glycol antifreezes with water proved to be an important factor, 70 to 80% of water causing maximum corrosion. The preferred non-freezing coolant of these types is water containing at least fifty percent by colume of any proprietary ethylene glycol antifreeze. These vary somewhat in corrosiveness depending on the inhibitors of iron corrosion employed. Sodium benzoate and certain oils were the most satisfactory inhibitors from the standpoint of aluminum cylinder heads. Kerosene showed promise as a non-corrosive, non-freezing coolant under special conditions.</div> <div class="htmlview paragraph">Inhibitors are sometimes used in tap water coolants to prevent rusting of the block and consequent clogging of the radiator. They cause corrosion of aluminum heads, even in the absence of antifreezes. Of the inhibitors tested in high chloride water, soluble oil was the least harmful to aluminum heads, and is therefore recommended where an inhibitor of iron corrosion must be used. Sodium benzoate has not yet been tested by the authors for such use but appears promising in view of the results reported by Vernon.<sup>(<span class="xref">1</span>)</sup> Chromates caused severe corrosion and their use with engines having aluminum cylinder heads and iron blocks cannot be too strongly condemned.</div> <div class="htmlview paragraph">If the engine manufacturer uses aluminum cylinder heads of the recommended alloy composition and condition, and a protective design of gasket, harmful corrosion will be avoided with only moderate attention to the recommendations concerning antifreezes and inhibitors.</div>

<div class="htmlview paragraph">Many computational methods have been suggested for the solution of this theoretical situation, such as Riemann variables, Lax-Wendroff and other finite difference procedures. The basic approach adopted here is to re-examine the fundamental theory of pressure wave motion and adapt it to a mesh method interpolation procedure. At the same time the boundary conditions for inflow and outflow, such as the filling and emptying of engine cylinders, has been resolved for the generality of gas properties and in terms of the unsteady gas flow which controls those processes. The same generality of gas property and composition is traced throughout the pipe system. This change of gas property is very significant in two-stroke engines where the exhaust blowdown is followed by short-circuited scavenge air. Vitally important in this context is the solution for the continual transmission and reflection of pressure waves as they encounter both differing temperature gradients and gas properties, and both gradual and sudden changes of area throughout the engine ducting. Of equal importance is the ability of the calculation to predict the effect of internal heat generation within the duct or of external heat loss from it, and to be able to trace the effect of the ensuing gas temperature change on both the pressure wave system and the nett gas flow.</div> <div class="htmlview paragraph">The new theoretical approach is programmed for a computer and the physical dimensions of a Husqvarna 250 motocross engine are used as input data. The correlation of the theory with the measured pressure and performance characteristics is demonstrably good. Extended insight into the behaviour of the actual engine is described.</div> <div class="htmlview paragraph">One of the unusual aspects of this new approach to this necessarily very complex theoretical situation is that both the theory, and the computational method for its solution, is relatively easy to comprehend and to apply in practice.</div>

<div class="htmlview paragraph">The implementation of the IFP-developped Compressed Air Assisted Fuel Injection process (named IAPAC) on a two-stroke engine allows the introduction of the fuel separately from the scavenging air in order to minimize fuel short-circuiting. The IAPAC process does not require an external air pump since the compressed air used to atomize the fuel is supplied, at no expense, by the crankcase. The premixed charge is delivered directly into the cylinder with a high spray quality and its stratification, for optimized combustion, is controlled by a valve. This process, therefore, provides the advantages of the direct injection but uses conventional low-pressure automotive type injection technology with commercially available gasoline injectors.</div> <div class="htmlview paragraph">In earlier work, we showed how the qualities of light weight, compactness, high specific power, high efficiency and low emissions make this concept particularly well-adapted for future automotive applications.</div> <div class="htmlview paragraph">Marine engine exhaust emissions from most conventional 2-stroke engines are excessive, and future legislation will no doubt take this fact into account. In this paper,we show how IAPAC technology provides an interesting solution to significantly reduce the pollutant emissions and improve the fuel economy of 2-stroke outboard engines.</div> <div class="htmlview paragraph">A 3-cylinder 1,2 L marine outboard IAPAC 2-Stroke engine has been developed and extensively tested. The results obtained point out that, with maintained quality of compactness and power output, this new engine gives fuel consumption reductions of more than 25 % and unburned hydrocarbon emission reductions of 70 to 90 %.</div> <div class="htmlview paragraph">Pollutant emissions are evaluated according to the ICOMIA procedure and the results clearly show how the IAPAC system is well adapted to take optimum advantage of the two-stroke cycle principle in marine outboard engines applications.</div>

<div class="section abstract"><div class="htmlview paragraph">Due to the recent anti-pollution policies, the performance increase in Spark Ignition (SI) engines is currently under the focus of automotive manufacturers. This trend drives control systems designers to investigate accurate solutions and build more sophisticated algorithms to increase the efficiency of this kind of engines.</div><div class="htmlview paragraph">The development of a control strategy is composed of several phases and steps, and the first part of such process is typically spent in defining and investigating the logic of the strategy. During this phase it is often useful to have a light engine simulator, which allows to have robust synthetic combustion data with a low calibration and computational effort.</div><div class="htmlview paragraph">In the first part of this paper, a description of the control-oriented ANalytical Engine SIMulator (ANESIM) is carried out. The latest results about the zero-dimensional knock model presented in a previous paper and some interesting analytical equations which define the main mean-combustion indexes trends (for example maximum in-cylinder pressure, or Pmax, 50 percent fuel mass fraction burned angle, or MFB50, Indicated Mean Effective Pressure, or IMEP) as functions of engine speed and load are analyzed for the entire engine operating range. A detailed sensitivity analysis to the fitting order is presented and the final formulas are showed and used for the calibration.</div><div class="htmlview paragraph">The second part focuses on the model implementation in a Simulink environment and the resulting validation process of the analytic simulator carried out on a Gasoline Direct Injection (GDI) Turbo Charged (TC) engine. ANESIM performance is then tested by comparing the calculated and the experimental data, for both steady state and transient operating conditions.</div></div>

A fluid loop can be effective for cooling some distance from a pulse tube cooler or in applications that require vibration isolation from the cooled object. Space pulse tube coolers are very efficient, but like all regenerative high frequency Stirling and pulse tube coolers, the cold head needs to be located near the compressor in order to minimize the input power to the cooler. To provide the directional gas flow from the oscillating flow pulse tube cooler we added cold reed valves to the pulse tube cold block of our flight proven high efficiency cooler (HEC) so that cold gas could be circulated without the need for an additional circulation pump and additional heat exchangers to cool the gas. In this test an improved smaller cold valve than that previously reported was installed and the remote cooling and the parasitic heat loads were measured. The measurements are compared to those of our previously reported cold valve tests as well as warm reed valve tests that used a second circulator compressor and recuperative heat exchanger. The large improvement in remote cooling power relative to the previous cold valve tests will be described.

<div class="htmlview paragraph">Due to the requirements of the market, engine manufacturers and their suppliers must develop new products in a short lead time, with high quality, high reliability and lowest possible costs.</div> <div class="htmlview paragraph">A method to obtain a short lead time for a complicated aluminum cylinder head is the design in 3 D CAD and the use of simultaneous engineering.</div> <div class="htmlview paragraph">A practical example shows the design of a 16-valve cylinder head in 3 D CAD (Catia).</div> <div class="htmlview paragraph">The cylinder head supplier received a CAD-tape with the main dimensions such as valve locations, shape of the combustion chamber and ports and location of the bolts.</div> <div class="htmlview paragraph">A design team completed the cylinder head design in 3 D CAD in consideration of the needs for foundry technology, casting tool design and machining of the part.</div> <div class="htmlview paragraph">Special casting tools for the prototyping were manufactured parallel to the cylinder head design.</div> <div class="htmlview paragraph">It is shown, that by the use of 3 D CAD/CAM and simultaneous engineering the multitude of engineering tasks can be solved and prototypes delivered within 3 months.</div>

<div class="section abstract"><div class="htmlview paragraph">Two-stroke engines are used in several purposes, such as lawn mowers, chainsaws, power generators and for motorcycles in some dirt tracks competitions. In addition, small Wankel engines are used in snowmobiles, motorized paragliders and range extenders. Both types of engines are known for the great power produced per displacement, ideal for the purposes aforementioned, but its bigger emissions due to lubricating oil mixed with fossil fuels, such as gasoline, do not pass legislation's standards, which limits their use. In order to reduce emissions, tests with ethanol and castor oil, eco-friendly fuel and lubricant, respectively, will be presented to adequate these organic compounds to the engine's operation.</div></div>