Turbo-discharging is a novel approach that can better utilize the energy recoverable by a turbine (or series of turbines) mounted in the exhaust flow of internal combustion engines. The recovery of blowdown pulse energy in isolation of displacement pulse energy allows the discharging (depressurization) of the exhaust system to reduce engine pumping work and improve engine fuel economy. This is a novel approach to air system optimization that has previously been studied for naturally aspirated engines. However, to be successful, turbo-discharging should be applicable to turbocharged engines, as downsizing is a promising direction for future powertrain systems. This study uses one-dimensional gas dynamics modelling to explore the effect of turbo-discharging on a turbocharged gasoline engine, particularly focusing on the interaction with the turbocharging system. The results show that the peak engine torque is increased at low to mid speeds with high speed torque slightly reduced due to restrictions in engine breathing with low lift exhaust valves. The engine peak torque as a function of speed with a larger turbocharger and turbo-discharging was comparable to that of the smaller turbocharger without turbo-discharging. Fuel economy improvements were evident over most part-load regions of the engine map, with peak values varying from 2 to 7% depending on the baseline engine air system strategy. Hot trapped residual mass was consistently reduced across a large fraction of the engine map, with the exception of high power conditions, where the valve pressure drop effect dominated. This is expected to enable spark advance and further fuel economy benefit. The results from this study are promising and show that the use of some of the available exhaust gas energy for turbo-discharging in preference to turbocharging can have a positive effect on both part-load and full-load engine performance. There remains significant potential for further optimization with application of variable valve actuation and turbocharger control systems (for example, variable geometry turbines).
Reducing emissions from light duty vehicles is critical to meet current and future air quality targets. With more focus on real world emissions from light-duty vehicles, the interactions between engine and exhaust gas aftertreatment are critical. For modern engines, most emissions are generated during the warm-up phase following a cold start. For Diesel engines this is exaggerated due to colder exhaust temperatures and larger aftertreatment systems. The De-NOx aftertreatment can be particularly problematic. Engine manufacturers are required to take measures to address these temperature issues which often result in higher fuel consumption (retarding combustion, increasing engine load or reducing the Diesel air-fuel ratio).In this paper we consider an inner-insulated turbocharger as an alternative, passive technology which aims to reduce the exhaust heat losses between the engine and the aftertreatment. Firstly, the concept and design of the inner-insulated turbocharger is presented. A transient 3D CFD/FEM (Computation Fluid Dynamics/ Finite Element Modelling) simulation is conducted and predicts that external heat losses will be reduced by 70% compared to a standard turbocharger, i.e. non-insulated turbocharger. A 1D modelling methodology is then presented for capturing the behaviour of the inner-insulated turbocharger. This is important as conventional models based on isentropic efficiency maps cannot accurately predict turbine outlet temperature. The alternative model is essential to demonstrate benefits in system-level simulations. Experimental results are presented from a transient air-path testing facility to validate the 1D model and demonstrate the characteristics of the inner-insulated turbocharger. Finally, the validated 1D model is used within a powertrain optimization simulation to demonstrate an improvement in fuel consumption for iso-NOx emissions over a low load city cycle of up to 3%.The work was conducted under the THOMSON project which has received funding from the European Union's Horizon 2020 Program for research, technological development and demonstration under Agreement no. 724037. The project aims to increase the market penetration of 48V hybrid vehicles.
The electrification of powertrains is now the accepted roadmap for automotive vehicles. The next big step in this area will be the adoption of 48V systems, which will facilitate the use of technologies such as electric boosting and integrated startergenerators. The introduction of these technologies gives new opportunities for engine airpath design as an electrical energy source may now be used in addition to the conventional mechanical and exhaust thermal power used in super- and turbochargers. This work was conducted as part of the EU funded project “THOMSON” which aims to create a cost effective 48V system enabling engine downsizing, kinetic energy recovery, and emissions management to reduce the environmental impact of transportation. The paper presents a study on an electrified airpath for a 1.6L diesel engine. The aim of this study is to understand the design and control trade-offs which must be managed in such an electrified boosting system. A two-stage boosting system including an electric driven compressor (EDC) and a variable geometry turbocharger (VGT) is used. The air path also include low and high pressure EGR loops. The work was performed using a combination of 1D modelling and experiments conducted on a novel transient air path test facility. The simulation results illustrate the trade-off between using electrical energy from in the EDC or thermal energy in the turbocharger to deliver the engine boost pressure. For a same engine boost target, the use of the EDC allows wider VGT opening which leads to lower engine backpressure (at most 0.4bar reduction in full load situation) and reduced pumping losses. However, electricity consumed in EDC either needs to be provided from the alternator (which increases the load on the engine) or by depleting the state of charge of the battery. The location of charge air coolers (pre- or post-EDC) is also investigated. This changes the EDC intake temperature by 100K and the intake manifold by 5K which subsequently impacts on engine breathing. An experimentally validated model of a water charge air cooler model has been developed for predicting flow temperature.
Different air systems such as turbochargers (TC), hybrid boosting, turbo compounding and exhaust gas recirculation (EGR) are increasingly used to improve the thermal efficiency of internal combustion engines (ICE). One dimensional (1D) gas dynamic codes supports their development and integration by modelling the engine and air systems and reducing testing time. However, this approach currently relies on steady flow characteristic maps which are inaccurate for simulating transient engine conditions. This is a key weakness of using gas-stand measured maps in engine simulations. Performing TC mapping on an engine would in principle solve this problem, however engine-based mapping is limited by the engine operating range and on these facilities, high-precision measurements are challenging. In addition, simple turbocharging can no longer be constrained to an individual TC supplying boost air to an engine. Instead, modern downsized engines require air-path system making use of multiple components including TCs, mechanical superchargers, electrically driven compressors (EDCs), EGR paths and control valves. Thus studying multiple air systems requires an experimental test facility to understand how they work in synergy. This is also useful in developing empirical models to minimize test time. Therefore the aim of this paper is to present a novel experimental facility that is flexibly designed for evaluating air systems individually and also at the system level representing a complicated air path both in steady and transient condition. The advanced test facility is built around a 2.2 l diesel engine to test the above air systems which can isolate the thermal and load transients from engine pulsating flows. Removing the flow pulsation allows study of the system characteristics in a steady state. Several examples of component and system level tests including a two-stage air path comprising of a VGT (variable geometry turbine) TC and a 48V EDC with typical operating condition (provided by 1D modeling) are discussed.
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