A comparison of variable valve strategies at part load for throttled and un-throttled SI engine configurations

The presented work concerns the study of the fuel consumption and emissions benefits achieved at part load by employing a fully variable valve train in a 1.6L SI gasoline engine. The benefits achieved when using variable valve timing alone, and combined with an early intake closing strategy for un-throttled operation were explored in order to highlight the merits of throttle versus un-throttled engine operation in conjunction with variable valve timing and lift. In addition, particular interest was given to the presence of internal Exhaust Gas Recirculation (EGR) and its ability to reduce pumping loss at part load. An engine model employing multiple sub models to handle variable valve operation was constructed using a commercial gas dynamics engine code, allowing detailed analysis of three valve strategies. Using the engine model, a theoretical study validated by experimentally available data was carried out to study key valve timing cases. A detailed breakdown of the mechanisms present in each case allowed a comprehensive understanding of the influence of valve timing on gas exchange efficiency and fuel consumption

Investigation of cylinder deactivation and variable valve actuation on gasoline engine performance

Increasingly stringent regulations on gasoline engine fuel consumption and exhaust emissions require additional technology integration such as Cylinder Deactivation (CDA) and Variable valve actuation (VVA) to improve part load engine efficiency. At part load, CDA is achieved by closing the inlet and exhaust valves and shutting off the fuel supply to a selected number of cylinders. Variable valve actuation (VVA) enables the cylinder gas exchange process to be optimised for different engine speeds by changing valve opening and closing times as well as maximum valve lift. The focus of this study was the investigation of effect of the integration of the above two technologies on the performance of a gasoline engine operating at part load conditions. In this study, a 1.6 Litre in-line 4-cylinder gasoline engine is modelled on engine simulation software and simulated data is analysed to show improvements in fuel consumption, CO2 emissions, pumping losses and effects on CO and NOx emissions. A CDA and VVA operating window is identified which yields brake specific fuel consumption improvements of 10-20% against the base engine at engine speeds between 1000rpm to 3500rpm at approximately 12.5% load. Highest concentration of CO emissions was observed at between 4 to 5 bar BMEP at 4000rpm and highest concentration of NOx at the same load range but at 1000rpm.Findings based on simulation results point towards significant part load performance improvements which can be achieved by integrating cylinder deactivation and variable valve actuation on gasoline engines. Copyright © 2014 SAE International

Design of Variable Geometry Waste Heat Recovery Turbine for High Efficiency Internal Combustion Engine

This study was carried out for a 1.25L Zetec-SE DOHC engine model but its application is generic to gasoline engine (light-duty engine) applications. An ORC model with a radial turbine sub-model is implemented in a light-duty gasoline I.C engine model, to evaluate the impact of the ORC with VGT on the engine fuel consumption, net power output and finally the ORC system efficiency as compared to ORC with FGT. The results showed that VGT can improve ORC system efficiency and net power output by an unweighted point of 5.6% and 3.07kW respectively at partial to high load conditions while benefits are even higher at the lower loads therefore making it an attractive technology given its ability to recover low-grade heat and the possibility to be implemented in decentralized lower-capacity power plant

Radial turbine expander design for organic rankine cycle, waste heat recovery in high efficiency, off-highway vehicles

Although state-of-the-art, heavy duty diesel engines of today can reach peak thermal efficiencies of approximately 45%, still most of the fuel energy is transformed into wasted heat in the internal combustion process. Recovering this wasted energy could increase the overall thermal efficiency of the engine as well as reduce the exhaust gas emissions. Compared to other Waste Heat Recovery (WHR) technologies, Organic Rankine Cycle (ORC) systems are regarded favourably due to their relative simplicity and small back pressure impact on engine performance and fuel consumption. The key elements affecting the efficiency of the ORC system are the type of working fluid selected and the design of the expander. In this simulation study, a zero-dimensional, design code has been developed to explore the impact of two, common, refrigerant working fluids on the design of a radial turbine expander. In addition, an off-design turbine analysis has been applied in order to evaluate the performance of the expander in the ORC cycle at various engine operating points. Moreover, the evaluation of ORC-diesel engine on improving fuel consumption, brake power, brake torque and exhaust gas emissions is investigated. Compared to a conventional diesel powertrain system, WHR showed an up to 5.7 % increase in brake torque and brake power and a 5.4% reduction in the brake specific fuel consumption (bsfc). The results also showed that the working fluid selection and the expander speed are critical parameters on the performance of the proposed hybrid powertrain configuration

Turbocharger matching methodology for improved exhaust energy recovery

Current engine simulation codes rely on user-input turbine maps to predict the performance of turbocharged engines. These experimentally obtained maps are limited in range as they are typically obtained through the use of an aerodynamically limited turbine loading device, the compressor. In order to extend the range of the map for simulation, several fitting techniques are utilized in order to obtain the values of efficiency and mass flow over the entire range of pressure ratio for all speeds. This investigation compares predicted turbine maps, obtained from narrow ranges of pressure ratio with more reliable, wider maps obtained experimentally for the same turbines by replacing the compressor with a dynamometer. The outcome of this investigation can be used to improve the fitting of efficiency and mass flow rate curves in engine simulation software

Thermodynamic and technical criteria for the optimal selection of the working fluid in a mini-ORC

Waste energy recovery (WER) is a suitable solution to improve the fuel utilization of Internal Combustion Engines (ICEs) by producing an eco-friendly electrical power from an energy source currently wasted. Organic Rankine Cycle (ORC) technology has been developed in the past few years to generate electric power from medium temperature (500 K – 800 K) ICE wasted thermal sources. Working fluid selection represents the first step in the design of an ORC. At the state of the art, authors where not able to select a single optimal organic fluid. This is mainly because of the different thermodynamic conditions of the heat sources which offer wasted thermal energy. This paper proposes a procedure for the ORC system preliminary working fluid selection, which takes into consideration thermodynamics and design parameters of the system components. The study is applied to WER systems specifically designed as bottoming cycles to ICE for transport applications. However, the method is quite general and makes the model easily adaptable to different heat sources. A steady state thermodynamic model of the system is developed via the software MATLAB. A wide variety of organic fluids (OF), such as R245fa, Solkatherm (SES36) and hexane have been investigated to identify the candidate which offers the best recovery opportunity. Regeneration is also included in this work. Results show that recover thermal energy in the regenerator is an essential method to improve power recovery when applying ORC to WER systems. The effect of superheating on the system power output has been investigated as well. It is capable to increase the cycle power output only when coupled with regeneration. The paper shows that the addition of a bottoming ORC to the ICE is convenient both in terms of recovered electric power (up to 14% of the engine nameplate power) and heat source utilization rate (up to 11 % heat source conversion into electricity). In addition, it is shown that water offers lower performance with respect to organic fluids when considering single stage radial expanders

Hybrid electric vehicle performance with organic rankine cycle waste heat recovery system

This study examines the implementation of a waste heat recovery system on an electric hybrid vehicle. The selected waste heat recovery method operates on organic Rankine cycle principles to target the overall fuel consumption improvement of the internal combustion engine element of a hybrid powertrain. This study examines the operational principle of hybrid electric vehicles, in which the internal combustion engines operates with an electric powertrain layout (electric motors/generators and batteries) as an integral part of the powertrain architecture. A critical evaluation of the performance of the integrated powertrain is presented in this paper whereby vehicle performance is presented through three different driving cycle tests, offering a clear assessment of how this advanced powertrain configuration would benefit under several different, but relevant, driving scenarios. The driving cycles tested highlighted areas where the driver could exploit the full potential of the hybrid powertrain operational modes in order to further reduce fuel consumption

Modelling of Supersonic Combustion Systems for Sustained Hypersonic Flight

Through Computational Fluid Dynamics and validation, an optimal scramjet combustor has been designed based on twin-strut Hydrogen injection to sustain flight at a desired speed of Mach 8. An investigation undertaken into the efficacy of supersonic combustion through various means of injection saw promising results for Hydrogen-based systems, whereby strut-style injectors were selected over transverse injectors based on their pressure recovery performance and combustive efficiency. The final configuration of twin-strut injectors provided robust combustion and a stable region of net thrust (1873 kN) in the nozzle. Using fixed combustor inlet parameters and injection equivalence ratio, the finalized injection method advanced to the early stages of two-dimensional (2-D) and three-dimensional (3-D) scramjet engine integration. The overall investigation provided a feasible supersonic combustion system, such that Mach 8 sustained cruise could be achieved by the aircraft concept in a computational design domain

Active Control Turbocharger for Automotive Application: An experimental evaluation

The current paper presents the results from a comprehensive set of experimental tests on a prototype active control turbocharger. This is a continuing series of test work as part of the development of this new type of turbocharger. Driven by the need to comply to increasingly strict emissions regulations as well as a continuing strive for better overall performance the active control turbocharger is intended to provide an improvement over the current state-of-the-art in turbocharging. In this system, the nozzle is able to alter the throat inlet area of the turbine according to the pressure variation of each engine exhaust gas pulse thus imposing a substantially more ‘active’ form of control of the conditions at the turbine rotor inlet

Overview of boosting options for future downsized engines

Driven by a demand for better fuel economy and increasingly stringent emissions regulations over a wide range of customers and applications, engine manufacturers have turned towards engine downsizing as the most potent enabler to meet these requirements. With boosting systems becoming ever more numerous as the technical solutions to complex boosting requirements of the internal combustion engine increase, it is time for an overview of available and under development boosting technologies and systems and for a discussion of their relevance to downsizing efforts. The presented analysis shows that there are no standard solutions for all the different applications as the trends indicate a rising complexity to meet with the extreme boosting requirements predicted for the remainder of the decade. These trends include variable geometry, a shift from single to two (or more) stages, extensive actuation for bypassing exhaust flows, exhaust flow regulation and pulsating exhaust energy recovery, severe electrification and an extensive effort downstream from the turbine to capture waste heat after the principal turbocharger/supercharger system