Turbo-Discharging the internal combustion engine

This thesis reports original research on a novel internal combustion (IC) engine charge air system concept called Turbo-Discharging. Turbo-Discharging depressurises the IC engine exhaust system so that the engine gas exchange pumping work is reduced, thereby reducing fuel consumption and CO2 emissions. There is growing concern regarding the human impact on the climate, part of which is attributable to motor vehicles and transport. Recent legislation has led manufacturers to improve the fuel economy and thus reduce the quantity of CO2 generated by their vehicles. As this legislation becomes more stringent manufacturers are looking to new and developing technologies to help further improve the fuel conversion efficiency of their vehicles. Turbo-Discharging is such a technology which benefits from the fact it uses commonly available engine components in a novel system arrangement. Thermodynamic and one-dimensional gas dynamics models and experimental testing on a 1.4 litre four cylinder four-stroke spark ignition gasoline passenger car engine have shown Turbo-Discharging to be an engine fuel conversion efficiency and performance enhancing technology. This is due to the reduction in pumping work through decreased exhaust system pressure, and the improved gas exchange process resulting in reduced residual gas fraction. Due to these benefits, engine fuel conversion efficiency improvements of up to 4% have been measured and increased fuel conversion efficiency can be realised over the majority of the engine operating speed and load map. This investigation also identified a measured improvement in engine torque over the whole engine speed range with a peak increase of 12%. Modelling studies identified that both fuel conversion efficiency and torque can be improved further by optimisation of the Turbo-Discharging system hardware beyond the limitations of the experimental engine test. The model predicted brake specific fuel consumption improvements of up to 16% at peak engine load compared to the engine in naturally aspirated form, and this increased to up to 24% when constraints imposed on the experimental engine test were removed

Turbo-discharging turbocharged internal combustion engines

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)

Turbo-Discharging: Predicted Improvements in Engine Fuel Economy and Performance

The importance of new technologies to improve the performance and fuel economy of internal combustion engines is now widely recognized and is essential to achieve CO2 emissions targets and energy security. Increased hybridisation, combustion improvements, friction reduction and ancillary developments are all playing an important part in achieving these goals. Turbocharging technology is established in the diesel engine field and will become more prominent as gasoline engine downsizing is more widely introduced to achieve significant fuel economy improvements. The work presented here introduces, for the first time, a new technology that applies conventional turbomachinery hardware to depressurize the exhaust system of almost any internal combustion engine by novel routing of the exhaust gases. The exhaust stroke of the piston is exposed to this low pressure leading to reduced or even reversed pumping losses, offering >5% increased engine torque and up to 5% reduced fuel consumption. This method has the distinct advantage of providing performance and fuel economy improvements without significant changes to the structure of the engine, the combustion system or lubrication system. The Turbo-Discharging concept is introduced and analyzed. A combination of filling/emptying models and 1-D gas dynamic simulations were used to quantify the energy flows and identify optimum valve timings and turbomachine characteristics. 1-D gas dynamic simulation was then used to predict primary fuel economy benefits from Turbo-Discharging. Secondary benefits, such as extended knock limits are then discussed