Electric Turbocompounding Research Articles

Evaluation of CO2 reduction in SI engines with Electric Turbo-Compound by dynamic powertrain modelling

In the last years, the research effort of the automotive industry has been mainly focused on the reduction of CO2 and pollutants emissions. In this scenario, concepts such as the engines downsizing, stop/start systems as well as more costly full hybrid solutions and, more recently, Waste Heat Recovery technologies have been proposed. These latter include Thermo-Electric Generator (TEG), Organic Rankine Cycle (ORC) and Electric Turbo-Compound (ETC) that have been practically implemented on few heavy-duty applications but have not been proved yet as effective and affordable solutions for passenger cars.The paper deals with the analysis of opportunities and challenges of the ETC for a compact car, powered by a turbocharged SI engine. The ETC consists of a motor-generator unit (MGU) integrated into the turbo shaft that can operate either as generator or motor. In the paper the benefits achievable by the electric turbo-compound have been investigated by simulation analyses carried out by a dynamic engine-vehicle model, validated against steady-state and transient experimental data. The in-cylinder processes and friction losses of the engine are modelled by a black-box parametric approach while grey-box dynamic models are applied for intake/exhaust manifolds and turbocharger to simulate more realistically the effect of ETC on engine performance and fuel economy along vehicle transients.The simulations have been carried out considering standard driving cycles (i.e. NEDC, WLTC) and several ETC management strategies. The results evidence that significant improvement of fuel economy and CO2 reduction can be achieved by suitable management of ETC operation, depending on engine speed and load and auxiliaries demand.

Heavy-duty engine electric turbocompounding

This paper analyses the performance of a heavy-duty engine when integrating a turbocompound system including a low-pressure-ratio turbine. The main feature of the low-pressure-ratio turbine is that of achieving efficiencies greater than 75% at very low pressure ratios (of approximately 1.1). The engine performance is predicted by a one-dimensionanl simulation model of a 10 l heavy-duty engine. An electric turbocompound system with a low-pressure-ratio turbine is fitted downstream of the main turbocharger to extract the exhaust gas energy. This additional energy supplies the electronic units and batteries. A method to scale an existing low-pressure-ratio turbine, designed for a 1.0 l gasoline engine, is defined and the changes in the turbine losses and the blade stresses are discussed. Low-pressure-ratio turbines of different sizes are analysed and compared in order to obtain the greatest benefit. In all cases the sum of the engine power and the turbocompound power is matched to the baseline engine power output. The full-load results show a power output from the low-pressure-ratio turbine of up to 15.8 kW, an improvement in the brake specific fuel consumption of the engine of up to 4% and a reduction in the brake mean effective pressure of up to 5%. The recovered exhaust gas energy is higher than the engine power required to balance the increased back pressure due to the additional component within the exhaust system. The electrical power produced is sufficiently high to replace the alternator.

A review and selection of engine waste heat recovery technologies using analytic hierarchy process and grey relational analysis

In this paper, a brief review and comparison of the engine waste heat recovery technologies have been made. These five technologies are electric turbocompounding systems (ETC), thermodynamic organic Rankine cycle (ORC), thermoelectric generators (TEG), hydrogen generation by using exhaust gas heat energy, and hybrid pneumatic power systems (HPPS). According to comparison results, the HPPS system can achieve the highest fuel economy improvement among the five technologies. Though there are their own benefits by utilizing these different technologies, their disadvantages prevent the application of these advanced technologies to different extent. Besides, a combined evaluation method consisting of grey relational analysis and analytic hierarchy process has been applied to assess the five new engine waste heat recovery technologies from the perspective of technical, economic, and environmental aspect. Based on the final results of the new evaluation method, the HPPS was found to be the most promising WHR technology for vehicle engines. But because of the emphasis on economic benefit, TEG was found to be more favorable for working conditions, like power plant and marine engine. What is more, as is shown in the sensibility analysis, the weighing of the environment relevant factors can prominently influence the comparison results between ETC and HPPS.

Characterisation of a low pressure turbine for turbocompounding applications in a heavily downsized mild-hybrid gasoline engine

This paper describes the outcomes of a study carried out on a novel exhaust energy recovery system for a heavily downsized gasoline engine. The investigation was carried out based on a 1.0 L turbocharged gasoline engine offering the same performance as a 2.0 L model, with the aim of reducing CO2 emissions from 169 g/km to 99 g/km. This is to be obtained by the synergistic application of electrified boosting, stop/start technology, regenerative braking, torque assist and exhaust energy recovery systems.The research focussed on the design of a high performance LPT (Low Pressure Turbine) to recover latent energy left in the exhaust gas after expanding in the main turbocharger turbine. The LPT is meant to be coupled to an electric generator whose combination is usually referred as electric turbocompounding. Given the small engine size and therefore the low mass flow rate of the exhaust gas, the design operating conditions were fixed at 50,000 rpm with an optimum pressure ratio of PR ≈ 1.1. Commercially available turbines are not suitable for this purpose due to the very low efficiencies (less than 40%) experienced when operating in such low pressure ratios range. The design was accomplished by following a number of steps which go from meanline loss model development, full 3-D CFD (Computational Fluid Dynamics) analysis (using ANSYS CFX), prototype manufacturing and steady-state testing. The test results, that were conducted by using the Imperial College London cold-flow test facility, showed good agreement with CFD analysis with an efficiency greater than 70%.The steady maps obtained from testing were then input into a 1-D engine model including the electric turbocompounding. Three different arrangements were considered for the turbocompounding: (1) pre-catalyst, (2) post-catalyst and (3) in the wastegate of the main turbocharger. Two different scenarios were investigated in which the extra energy recovered by the turbocompounding unit is either fully regenerated into the engine crankshaft or stored and not re-used. The BSFC (brake specific fuel consumption) and the BMEP (brake mean effective pressure) were calculated and compared with the baseline engine under full and part load conditions. At full load, the analysis was performed for several engine speeds (from 1000 rpm to 6000 rpm at steps of 500 rpm each). The results showed that the extra energy recovered by the turbocompounding device is offering a significant benefit on engine performance; the post-catalyst solution offers the best compromise in terms of BSFC and BMEP with an improvement of 2.41% and 2.21% respectively. At part load engine instead, the analysis was performed for three engine speeds (1500 rpm, 2000 rpm and 4000 rpm) for the post-catalyst position only. Despite the increment in pumping work due to the presence of the LPT, no significant penalty in BSFC was calculated when no energy is returned into the engine whereas an improvement of ≈2.64% was found in the other case.

Simulation of a heavy-duty diesel engine with electrical turbocompounding system using operating charts for turbocharger components and power turbine

In diesel engines, approximately 30–40% of the energy supplied by the fuel is rejected to the ambience through exhaust gases. Therefore, there is a potentiality for further considerable increase of diesel engine efficiency with the utilization of exhaust gas heat and its conversion to mechanical or electrical energy. In the present study, the operational behavior of a heavy-duty (HD) diesel truck engine equipped with an electric turbocompounding system is examined on a theoretical basis. The electrical turbocompounding configuration comprised of a power turbine coupled to an electric generator, which is installed downstream to the turbocharger (T/C) turbine. A diesel engine simulation model has been developed using operating charts for both turbocharger and power turbine. A method for introducing the operating charts into the engine model is described thoroughly. A parametric analysis is conducted with the developed simulation tool, where the varying parameter is the rotational speed of power turbine shaft. In this study, the interaction between the power turbine and the turbocharged diesel engine is examined in detail. The effect of power turbine speed on T/C components efficiencies, power turbine efficiency, exhaust pressure and temperature, engine boost pressure and air to fuel ratio is evaluated. In addition, theoretical results for the potential impact of electrical turbocompounding on the generated electric power, net engine power and relative improvement of brake specific fuel consumption (bsfc) are provided. The critical evaluation of the theoretical findings led to the basic conclusion that there is a significant potential for bsfc improvement of HD diesel truck engines with the proposed electrical turbocompounding concept, which reaches up to 4% at full engine load. The improvement of bsfc with electric turbocompounding appears to be more attractive solution in terms of technical complexity and installation cost against other competitive heat recovery technologies such as Rankine cycle systems.