Mathieu Picard

Rim-Rotor Rotary Ramjet Engine, Part 2: Quasi-One-Dimensional Aerothermodynamic Design

The rim–rotor rotary ramjet engine is a new propulsion-system design with the potential to significantly improve power density and reduce complexity over conventional gas turbines, thus making it an interesting alternative for future transportation and stationary power systems. This paper presents a quasi-one-dimensional aerothermodynamic design model, taking into account the dominant physics of the rim–rotor rotary ramjet engine: 1) shock-wave compression, 2) high-g field combustion, 3) viscous losses, 4) heat transfer, 5) inlet and outlet periodic condition, and 6) windage losses. It is shown that high flame velocity due to buoyant forces leads to a very compact combustion chamber and possibly very low nitrogen oxides. A 500 kW rim–rotor rotary-ramjet-engine version is designed with the model and could produce 7:6 kW=kg at a tangential velocity of 1000 m=s, which is more than twicetheactualgas-turbinepowerdensity.Aproof-of-conceptprototypeistestedatlowspeed(Mach1),andshows good agreement with the model for both indicated power without combustion and windage losses. Combustion efficiency is measured to over 85% at 220;000g. These results confirm the design model capabilities, at least within the range of tested Mach numbers.

Design and Experimental Validation of a Supersonic Concentric Micro Gas Turbine

This paper presents the design and experimental results of a new micro gas turbine architecture exploiting counterflow within a single supersonic rotor. This new architecture, called the supersonic rim-rotor gas turbine (SRGT), uses a single rotating assembly incorporating a central hub, a supersonic turbine rotor, a supersonic compressor rotor, and a rim-rotor. This SRGT architecture can potentially increase engine power density while significantly reducing manufacturing costs. The paper presents the preliminary design of a 5 kW SRGT prototype having an external diameter of 72.5 mm and rotational speed of 125,000 rpm. The proposed aerodynamic design comprises a single stage supersonic axial compressor, with a normal shock in the stator, and a supersonic impulse turbine. A pressure ratio of 2.75 with a mass flow rate of 130 g/s is predicted using a 1D aerodynamic model in steady state. The proposed combustion chamber uses an annular reverse-flow configuration, using hydrogen as fuel. The analytical design of the combustion chamber is based on a 0D model with three zones (primary, secondary, and dilution), and computational fluid dynamics (CFD) simulations are used to validate the analytical model. The proposed structural design incorporates a unidirectional carbon-fiber-reinforced polymer rim-rotor, and titanium alloy is used for the other rotating components. An analytical structural model and numerical validation predict structural integrity of the engine at steady-state operation up to 1000 K for the turbine blades. Experimentation has resulted in the overall engine performance evaluation. Experimentation also demonstrated a stable hydrogen flame in the combustion chamber and structural integrity of the engine for at least 30 s of steady-state operation at 1000 K.

High-g Field Combustor of a Rim–Rotor Rotary Ramjet Engine

High-g field combustion, such as in rotary ramjet engines, is a promising approach to reduce nitride oxides and combustor size by taking advantage of the flame acceleration due to the buoyancy of the products over the reactants. This paper presents a high-g field combustor design for a rim–rotor rotary ramjet engine. In this device, a premixed flow of air and fuel is ignited in the nonrotating inlet track and then swallowed and stabilized in the rotating combustion chamber. Outboard ignition frees the rotating structure from igniters, increasing the maximal tangential speed of the engine and thus its maximal efficiency. The rotating combustor design benefits from extreme centrifugal fields (105g to 107g) for both stabilizing the flame during ignition and maximize flame velocity. A simple buoyancy-driven combustion model allows estimating the combustor length and shows good agreement with numerical simulations, which demonstrate a combustion efficiency to be higher than 85%, even with some reactants bypass...

Performance of a Low-Blowby Sealing System for a High Efficiency Rotary Engine

The X engine is a non-Wankel rotary engine that allies high power density and high efficiency by running a high-pressure Atkinson cycle at high speeds. The X engine overcomes the gas leakage issue of the Wankel engine by using two axially-loaded face seals that directly interface with three stationary radially-loaded apex seals per rotor. The direct-interfacing of the apex and face seals eliminates the need for corner seals of the typical Wankel engine, significantly reducing rotary engine blowby. This paper demonstrates the sealing performance that can be achieved by this new type of seal configuration for a rotary engine based on dynamics models and experiments. The dynamics models calculate the displacement and deformation of the face and apex seals for every crank angle using a time implicit solver. The gas leakage is then calculated from the position of the seals and pressure in the chambers and integrated over a rotor revolution. An “effective leakage orifice” area can be determined, to compare blowby between different engine types. Model results show that the X engine equivalent leakage area could be around 35% that of the leakage area of a similarly sized Wankel engine obtained from the same modeling method, which brings the X engine leakage closer to the piston engine’s leakage range. Initial experimental results support the findings from the model, as the X engine shows an equivalent leakage area of about 65% that of a scaled Wankel engine. This result demonstrates the potential of the X engine to achieve gas sealing improvements through additional seal development. Introduction For applications that need a high power density, the rotary engine has been an interesting candidate since its debut in the 1950s. In addition to its impressive power density, it also features fewer moving parts and lower vibrations levels compared to piston engines. However, it has seen a decrease in popularity in recent years, notably in the automotive industry, with the last remaining Wankel engine powered car being manufactured in 2012. The withdrawal of rotary engines from the automotive market can be explained by the traditional drawbacks of rotary engines, along with increasing emission regulations around the globe. An important drawback of the rotary engines is the difficulty to seal the combustion chamber. The Wankel engine’s geometry requires radially loaded apex seals as well as axially loaded face seals, and the interface between these is not effectively sealed which leads to increased leakage. Various scientific work has been done on the Wankel type rotary engines since the 1950’s. The sealing performance of the Wankel engine was studied both experimentally and by modeling. Different methods were used to simulate the Wankel engine by the past, such as modifying piston engines commercial simulation softwares [1], by the use of CFD tools [2], or by analytical calculations [3, 4]. Throughout the literature, the seal leakage values are usually quantified as an equivalent orifice area, which is not directly linked to the dynamics of the seals. This leakage area is usually determined by fitting a full engine cycle simulation model to experimental in-cylinder pressure and other data, tuning parameters such as compression ratio, port flow coefficients, heat transfer multipliers, and leakage orifice areas. For a Mazda Wankel, Eberle and Klomp [5] determined a leakage area value of 2 mm2 per cell, while others [6]-[8] found 1 mm2. In an effort to better understand the behavior of the Wankel seals, models were created to study the dynamics of the seals [9]-[12]. The seal model by Picard [3, 4] successfully relates the sealing performance to the dynamics and deformation of the seals to predict leakage. The final results of the model predict an equivalent leakage area varying between 1 mm2 and 2 mm2 for the Renesis engine. The main conclusion of these studies is that the seals tend to leak near the extremities of the parts that interact with each other. In a piston engine, since the rings only have a single gap, they are able to achieve better sealing performances than Wankel engines. The X Engine is a rotary engine with an alternative architecture that has the potential to solve the rotary engine sealing Downloaded from SAE International by Alexander Shkolnik, Sunday, May 27, 2018

Fabrication and Demonstration of Planar Micro-Reactors for Solar Steam Methane Reforming

This paper presents a novel solar micro-reactor architecture for cheap hydrogen production by methane reforming. Using microfabrication techniques to create three-dimensional channel networks in diffusion-bonded plates, all the sub-processes required for methane reforming are integrated in a small unit, which is well suited for implementation on cheap and well-established solar parabolic troughs. Monolithic integration of the sub-processes allows heat recovery from the high temperature reaction to the lower temperature endothermic processes such as water vaporization and reagent preheating. To demonstrate the manufacturing feasibility as well as the sufficient catalytic activity, a 4.5W stainless steel demonstrator is built and tested in the laboratory. Results show a complete methane conversion for temperatures over 850°C at a space velocity of 35 000 ml/h*mlcat.

Shock-Induced Combustion and Its Applications to Power and Thrust Generation

Due to the high pressure and temperature state produced by shock waves, they offer the possibility to greatly speed up combustion processes as compared to diffusive reaction mechanisms. Devices exploiting shock-induced combustion also have the potential for higher compression ratios, and thus better efficiency, and less complexity than systems using mechanical compression systems. These advantages can lead to lighter, more efficient, and more compact propulsion and power systems.