Browse Topic: Rotary engines
Mazda, the automaker with the longest and richest history of using the Wankel rotary engine announced that it resumed mass production of rotary engines for a new variant of the MX-30 compact crossover. Mazda provided little detail about the engine itself, which serves as a generator for the MX-30 e-SKYACTIV R-EV, a plug-in hybrid (PHEV) variant of the MX-30 crossover. Mazda hasn't used the unique powerplant for a production vehicle for more than a decade. The MX-30 e-SKYACTIV R-EV employs the rotary engine in a series-hybrid layout to generate electricity to replenish the vehicle's 17.8-kWh lithium-ion battery, which when fully charged, can provide up to 85 km (31 miles) of driving range on Europe's Worldwide Light Vehicle Test Procedure (WLTP) cycle. Gasoline from a 50-L (13.2-gal.) fuel tank supplies the rotary when its operation is required to provide electricity for extended-range driving. In a release, Mazda explained it “positioned it [the rotary engine] on the same axle as a high-output motor and a generator” in the front engine bay.
This paper details the design and components of a high-power density Hybrid-Electric Power generation testbed that is being built by the Eagle Flight Research Center at Embry-Riddle Aeronautical University, Florida. The system consists of a twin-rotor rotary Wankel engine, a radial flux Permanent Magnet Synchronous Machine used as the generator along with its inverter/controller, a 400 V Lead-acid battery pack, a vehicle control unit, and the associated thermal systems. The system weighs 324 lbs. (147 kg) before fuel and is estimated to achieve peak power of 134 hp (100 kW) with the High-Voltage battery and sustained power of 70 hp (52 kW) with just the hybrid-electric system. With 8 gallons of fuel, the system is estimated to realize a specific energy of 0.37 hp-h/lb. (0.61 kWh/kg), and a specific power of 0.46 hp/lb. (0.76 kW/kg). The system control was implemented on the Vehicle Control Unit using a feedforward-feedback control loop with user-defined speed and output power values.
Today unmanned aerial vehicle applications are powered by Wankel rotary engines due to their high power-to-weight ratio and smooth operation. Most of modern propulsion units for unmanned aerial vehicles are designed to run on high volatile fuels such as aviation gasoline (AvGas). However, the refueling infrastructure in aviation is geared toward the most used aviation fuel, kerosene. This and other reasons, such as significantly lower price and easier fire protection regulations, lead to the desire to be able to operate these propulsion units with kerosene. Opposed to reciprocating engines, the low compression ratio of rotary engines prevents the implementation of compression ignition combustion processes. Therefore, the purpose of this paper is to discuss the operation of a spark-ignited rotary engine on different fuels. In detail, different qualities of kerosene as well as gasoline/kerosene blends are compared together. In this respect, a thermodynamic analysis of the individual operations is undertaken. In order to make a statement about the efficiency and quality of the combustion, the investigation is carried out to determine the optimal rotor angle range for the center of combustion, with maximal efficiency and torque. On the basis of measurement data, it was possible to show that rotary engines also have an optimal rotor angle for the center of combustion, almost regardless of the operating point and mixture composition. Only the fuel used has little influence on the location of the optimal center of combustion. In addition to the comparison of the combustion characteristics of the individual fuels, the problems of operating with kerosene are examined in detail. Due to the low knock resistance of kerosene, restrictions in the operational area can be observed. Nevertheless, despite the different properties of the fuels, approximately similar torques and power outputs can be generated.
The present work investigates a means of controlling engine hydrocarbon startup and shutdown emissions in a Wankel engine which uses a novel rotor cooling method. Mechanically the engine employs a self-pressurizing air-cooled rotor system (SPARCS) configured to provide improved cooling versus a simple air-cooled rotor arrangement. The novelty of the SPARCS system is that it uses the fact that blowby past the sealing grid is inevitable in a Wankel engine as a means of increasing the density of the medium used for cooling the rotor. Unfortunately, the design also means that when the engine is shutdown, due to the overpressure within the engine core and the fact that fuel vapour and lubricating oil are to be found within it, unburned hydrocarbons can leak into the combustion chambers, and thence to the atmosphere via either or both of the intake and exhaust ports. As well as shutdown it also affects the startup process, where higher hydrocarbon emissions are caused due to the forced transfer of the unburned gases to the intake and exhaust ducts as the core depressurizes across the sealing grid when it is stationary. These emissions then sit in those volumes, possibly then escaping to the outside world; clearly this is also very important with respect to the SHED testing of any vehicle the engine might be fitted to. The SPARCS concept is discussed with respect to how it functions versus a conventional wet sump arrangement (as employed by oil cooled rotor Wankel engines). Measurements are taken and steady-state emissions and fuel consumption results with and without pressurization of the core are presented; such a comparison has not been made before. In general, power output, brake specific fuel consumption, hydrocarbon emissions, and combustion efficiency are all better with a depressurized core, with only small improvements in cooling (defined by rotor air inlet temperature) being apparent when it is pressurized. A hypothesis for why this should be so is developed, the knowledge of which can help to guide further development. The reasons for the engine on/off hydrocarbon issue are apparent. Using a solenoid valve as a means of venting the rotor core pressure directly to the engine intake just before shutdown is proposed as a means of alleviating this problem. This approach would feed the hydrocarbon-rich gases from the core through the combustion process and out through the catalytic converter just before the engine is switched off. In automotive applications this engine is to be used as a range extender and hence there is a great degree of control regarding all modes of its operation, including startup and shutdown, which is the approach investigated for mitigation here. The results show that depressurizing the core in this manner results in a maximum reduction in total hydrocarbon emissions during warm shutdown and restart of 80% and 60%, respectively. However, it must be remembered that with the pressure relieved in the core, the cooling capability there is slightly reduced, and so the approach has to be calibrated correctly to achieve the best result for the whole system. Further investigation into the optimum level of pressurization is recommended.
Wankel rotary engines (REs) are often used for unmanned aerial vehicle (UAV) applications due to their excellent power-to-weight ratio and their smooth operation. Existing RE propulsion units are mainly designed to run on high-volatility fuels like aviation gasoline or regular gasoline. However, specific applications require a jet fuel or even multi-fuel capability. Due to their geometry, the low compression ratio (CR) of REs prevents the implementation of compression ignition (CI) combustion processes. While publications of modified spark-ignition engines that are able to run on low-volatile fuels are already few in number, publications of heavy-fuel spark-ignited (SI) REs can hardly be found at all. The purpose of this paper is as follows: The operation of a SI RE operated on kerosene is discussed. Accordingly, a thermodynamic analysis is carried out at warmed-up operation with kerosene. It is shown that sufficient performance and power output can be achieved on kerosene for full-load behavior. Furthermore, cold-start tests are carried out to investigate the limits of kerosene operation. Therefore, a low-temperature test bench is developed that allows the investigation of engine starts down to −30°C. The challenges of mixture formation for heavy fuels in port fuel injection systems for REs at cold-start conditions are investigated and discussed. It is demonstrated that cold starting a SI RE down to −25°C is possible with correct measures.
In a previous study it was shown that a production vehicle employing a Wankel rotary engine, the Mazda RX-8, was easily capable of meeting much more modern hydrocarbon emissions than it had been certified for. It was contended that this was mainly due to its provision of zero port overlap through its adoption of side intake and exhaust ports. In that earlier work a preliminary investigation was conducted to gauge the impact of adopting a zero overlap approach in a peripherally-ported Wankel engine, with a significant reduction in performance and fuel economy being found. The present work builds on those initial studies by taking the engine from the vehicle and testing it on an engine dynamometer. The results show that the best fuel consumption of the engine is entirely in line with that of several proposed dedicated range extender engines, supporting the contention that the Wankel engine is an excellent candidate for that role. Also, continued 1-D modelling of the zero overlap peripherally-ported engine has shown that a potential route to regain lost performance and better fuel economy is to turbocompound the engine. While compounding using turbomachinery provides one direction for further work, a new concept is proposed which uses the conventional three-flank Wankel rotor in its two-lobe housing to provide a positive displacement compounder to enable zero overlap anywhere in the device. This will allow the potential to configure large unobstructive ports with unimpeded timing. This novel concept is discussed in the paper.
The growing need for a sustainable worldwide mobility is leading towards a paradigm shift in the automotive industry. The increasingly restrictive regulations on vehicle emissions are indeed driving all of the world-leading road vehicles manufacturers to redesign the concept of transportation by developing new propulsion solutions. To this aim, a gradual electrification strategy is being adopted, and several hybrid electric solutions, such as extended-range electric vehicles with reciprocating engines or fuel cells, already represent a valid alternative to conventional vehicles powered by fossil fuels. Despite their appealing features, these hybrid propulsion systems present some drawbacks, mainly related to their complex architecture, causing high overall dimensions, weight and costs, which pose some limitation in their use for small-size vehicles. In this context, the Wankel engine may bring significant advantages, since it is characterized by an extremely compact and light design, it has excellent noise and vibration features, and it is potentially cheap to manufacture. As a consequence, the use of a rotary engine as range extender in hybrid propulsion systems represents a very attractive option, especially for small-size vehicles. In addition, the Wankel engine is particularly well suited to be powered by hydrogen fuel. In fact, hydrogen fuel, besides bringing clear advantages on the overall vehicle emissions, may diminish the inherent combustion difficulties that are caused by the shape of the combustion chamber of a rotary engine. Thus, in this work, we model a hydrogen-fueled rotary engine configuration to evaluate its potential as auxiliary power unit in ultra-low emission small-size hybrid vehicles. Starting from a baseline series hybrid electric vehicle with reciprocating internal combustion engine, we replace the range extender to numerically investigate on the performance of the proposed solution, in terms of energy and fuel consumption. The weight saving due to the use of Wankel engine is compensated by introducing additional battery modules, in such a way to keep the original weight of the baseline vehicle as a fixed parameter. Different range extender options are also analyzed for comparison, including a reciprocating and a rotary engine both fueled by gasoline.
The current quest to reduce CO2 emissions combined to new technologies has sparked an interest in revisiting radically different engine configuration concepts, such as adiabatic and split-cycle engines. To achieve the full potential of both concepts, the combustion chamber must be sealed without lubricating oil. A promising approach that has yet remained elusive, is to lubricate the piston-liner interface with gases. This paper explores the concept of using non-contacting finger seals to seal piston engines combustion chambers. The finger seals, made of a gas-lubricated pad at the end of a flexible beam, are fixed on a rotating piston that uses the centrifugal force to close the piston-liner gap. A physics-based fluid-structure model is developed to predict finger displacements and sealing performances. The model shows that the radial displacement of the fingers naturally creates a convergent profile with the liner that generates sufficient aerodynamic pressure to maintain a micrometer gap that prevents the piston to contact the liner. The results also show that the achievable leakage area would be similar to that of Wankel rotary engine and friction losses would be negligible compared to those of conventional piston rings. On the other hand, the study reveals challenges that will need to be addressed in order that finger seals be practical in engines, such as the finger torsion, dynamic behavior when exposed to bore distortion as well as the manufacturing tolerances required to ensure contact-free operation.
The use of Wankel rotary engines as a range extender has been recognised as an appealing method to enhance the performance of Hybrid Electric Vehicles (HEV). They are effective alternatives to conventional reciprocating piston engines due to their considerable merits such as lightness, compactness, and higher power-to-weight ratio. However, further improvements on Wankel engines in terms of fuel economy and emissions are still needed. The objective of this work is to investigate the engine modelling methodology that is particularly suitable for the theoretical studies on Wankel engine dynamics and new control development. In this paper, control-oriented models are developed for a 225CS Wankel rotary engine produced by Advanced Innovative Engineering (AIE) UK Ltd. Through a synthesis approach that involves State Space (SS) principles and the artificial Neural Networks (NN), the Wankel engine models are derived by leveraging both first-principle knowledge and engine test data. We first re-investigate the classical physics-based Mean Value Engine Model (MVEM). It consists of differential equations mixed with empirical static maps, which are inherently nonlinear and coupled. Therefore, we derive a SS formulation which introduces a compact control-oriented structure with low computational demand. It avoids the cumbersome structure of the MVEM and can further facilitate the advanced modern control design. On the other hand, via black-box system identification techniques, we compare the different NN architectures that are suitable for engine modelling using time-series test data: 1) the Multi-Layer Perceptron (MLP) feedforward network; 2) the Elman recurrent network; 3) the Nonlinear AutoRegressive with eXogenous inputs (NARX) recurrent network. The NN models overall tend to achieve higher accuracy than the MVEM and the SS model and do not require a priori knowledge of the underlying physics of the engine.
The paper first includes the main objective and boundary conditions for design and simulation of a multi fuel gas mixture system of a Wankel rotary engine. New regenerative fuels are more and more important for use in automotive propulsion and stationary applications of combustion engines. Due to the special design and operation of rotary engines there are opportunities for running these engines in future electric and hybrid applications with new designed liquids and gaseous fuels based on regenerative energy sources. Nevertheless, rotary engines have advantages in avoidance of preignition and detonation especially when using gaseous fuels with a higher percentage of hydrogen. The focus is on basic research and analyses of main physical and thermodynamic properties of separate lean burn gases (lower calorific value, mixed calorific value, AFR) and their effects on fuel mixing and engine performance. Furthermore, the scope of the investigation is on the development of simulation models, which are capable to simulate the entire engine process and to map all factors influencing mixture formation, and for the combustion important parameter of unconventional gaseous fuels. Moreover, the authors compare analytical methods and modeling of the power estimation and fuel mixing with 1d simulations of the fuel mixing and rotary engine thermodynamic performance. Analytical models and calculations estimate the effective power and the dimensioning of the mixture formation system. Later on there is a special focus on the modelling of a rotary engine with a commercial reciprocating engine simulation tool that needs significant modifications for calculation of rotary engines. For this work, the authors created a new substitute cylinder model for running the special rotary engine thermodynamic process. The simulation contains the optimization of port timing combined with the intake and exhaust pipes. Finally, the mixture formation system has been coupled with the engine process. The results of the simulations and the analytical methods show the effects of separate design and thermodynamic parameters in combination with regenerative gaseous fuel on the volumetric efficiency, residual gas fraction and scavenging fraction. The work makes a fundamental contribution to the use of novel fuels in conjunction with specially designed internal combustion engines.
Currently automotive engines are reciprocating or Wankel rotary engine types. Reciprocating engines are bulky, heavy and complex, mainly due to the intake and exhaust valves and their associated cam-train. Wankel engines have a low rotor rev limit, and have inefficient sealing of the apex seals leading to poor economy and undesirable emission gases. The Rotary Engine Development Agency (REDA) has designed a new three-chamber rotary internal combustion engine concept using an adaptation of the patented Szorenyi Curve. The new design is an evolution of the design which was the subject of SAE Technical Paper 2017-01-2413 and SAE publication ‘So You Want to Design Engines: UAV Propulsion Systems’. This paper describes the features of the new three-chamber engine concept and includes an analysis of the major shortcomings of the Wankel engine. The Wankel engine’s geometry results in excessive crankshaft deflection at high engine revs due to the centrifugal force of the rotor which is eccentric to the crankshaft. This results in a low rotational speed limit. Analysis of the Wankel design reveals that the rotational speed limit cannot be increased by increasing the diameter of the crankshaft. Also, analysis of the apex seal reveals that the shape of the stator accelerates the seal inwards during the intake and power stroke and, at the same time, the seal experiences a large change in its contact angle with the stator surface. These effects combine to produce poor conditions for sealing the combustion chamber of the Wankel engine. The paper identifies that the Szorenyi three-chamber engine design does not have these same issues because its symmetrical rotor enables a high rotational speed, and its continuously concave stator profile ensures an outward acceleration of the apex seal and much less change of contact angle with the stator surface. The paper concludes that the Szorenyi engine has the potential to replace Wankel and reciprocating engines in a range of applications and is particularly suited to light aircraft.
The present work presents the concept of a new rotary engine, and provides first investigations for its implementation in the energy sector. The main focus of this work is to provide a theoretical description of the engine and its differences from the state-of-the-art technologies. Its innovative principle consists of concentric operation, with two pistons of different rotation radius and the addition of a third intermediate chamber between the compression and combustion chamber. A description of the engine’s physical model is provided, followed by an analysis of the selected specific geometrical features. Additionally, a thermodynamic analysis clarifies the operational advantage compared to the existing cycles and, finally, a numerical investigation on the engine’s bulk performance is provided to quantify the anticipated results of the theoretical analysis. The theoretical description concludes that the new rotary engine is characterized by simple design with the minimum possible moving parts that can be easily integrated into hybrid systems or small sized applications. Its anticipated volume and weight is five to six times smaller than that of conventional engines owing to the fact that there is no need for motion conversion system and there is one power stroke in every 180 degrees. Last but not least, its expected thermal efficiency based on Atkinson cycle can theoretically be 15% greater than that of existing engines for the same application.
VRDE has developed Wankel type rotary engine to achieve high power output & fuel efficiency for indigenization programme of UAVs. This engine is meeting all performance parameters needed for intended aerial vehicle. This paper describes the testing methodology followed by development engineers to prove the endurance and reliability of UAV engine for airworthiness certification. This paper gives the brief about testing carried out on the Wankel engine, failures faced during endurance testing and their rectification to enhance the life of the engine to achieve hundred test cycle mark. This paper also briefs about the test set up, endurance test cycles simulating the practical operating conditions.
Energy independence and reduction in pollutant emissions are a center of interest for several researchers and car manufacturers. Renewable fuels have gained in popularity because of their sustainability and, in some cases, lower amounts of greenhouse gases. Moreover, energy diversification is also required by all countries. One possible solution is the use of biofuels such as ethanol, methanol, etc. These biofuels have been shown as good candidates as alternative fuels for vehicles because they are liquid and they have several physical and combustion properties similar to gasoline. Alcohols have also a higher octane number and oxygen content than gasoline. This allows the alcohol engines to have much higher compression ratios (CRs), and thus, better BTE (brake thermal efficiency). Brazilian car manufacturing industry has developed flexible-fuel vehicles, introduced in 2003, which became a commercial success. Flex fuel internal combustion engines (ICEs) can run on any proportion of Brazilian gasoline (E27 blend) and hydrous ethanol (E100), allowing the use of the cheaper fuel available. However, conventional flex fuel engines have a fixed CR, generally between the ideals CRs for gasoline and ethanol, which leads to lower BTE and higher fuel consumption. In order to reduce or eliminate these issues, this paper presents the Kopelrot engine, a flexible fuel rotary engine with dynamically variable compression ratio.
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