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The paper describes the design and development of ‘Sabre’, a 3-cylinder engine encompassing a combination of technologies to realise low CO2 in a practical automotive application while retaining driving pleasure (vehicle acceleration performance). This project is a partnership with Continental Automotive, in which Lotus Engineering is responsible for the base engine and combustion system. The decision process that led to a close-spaced direct injection combustion system that does not target high BMEP as the chief route to low fuel consumption is described. Instead of pursuing an approach in which specific power is maximized in order to reduce throttling losses at part load, mild downsizing coupled with throttling loss reduction and turbulence manipulation enabled by a switching valve train is employed.

The engine of a high performance sports car has been converted to operation on E85, a high alcohol-blend fuel containing nominally 85% ethanol and 15% gasoline by volume. In addition to improving performance, the conversion resulted in significant improvement in full-load thermal efficiency versus operation on gasoline. This engine has been fitted in a test vehicle and made flex-fuel capable, a process which resulted in significant improvements in both vehicle performance and tailpipe CO2 when operating solely on ethanol blends, offering an environmentally-friendly approach to high performance motoring. The present paper describes some of the highlights of the development of the flex-fuel calibration to enable the demonstrator vehicle to operate on any mixture of 95 RON gasoline and E85 in the fuel tank. It also discusses how through detailed development, the vehicle has been made to comply with primary pollutant emissions legislation on any ethanol-gasoline mixture up to E85.

The future exploitation of global energy resources is currently being hotly debated by politicians and by sections of the scientific community but there is little guidance available in the engineering literature as to the full gamut of options or their viability with respect to fuelling the world's vehicles. In the automotive industry extensive research is being undertaken on the use of alternative fuels in internal combustion engines and on the development of alternative powerplants but often the long-term strategy and sustainability of the energy sources to produce these fuels is not clearly enunciated. The requirement to reduce CO2 emissions in the face of accelerating global warming scenarios and the depletion of fossil-fuel resources has led to the widespread assumption that some form of ‘hydrogen economy’ will prevail; this view is seldom justified or challenged.

The paper discusses the use of alcohol fuels in high performance pressure-charged engines such as are typical of the type being developed under the ‘downsizing’ banner. To illustrate this it reports modifications to a supercharged high-speed sports car engine to run on an ethanol-based fuel (ethanol containing 15% gasoline by volume, or ‘E85’). The ability for engines to be able to run on alcohol fuels may become very important in the future from both a global warming viewpoint and that of security of energy supply. Additionally, low-carbon-number alcohol fuels such as ethanol and methanol are attractive alternative fuels because, unlike gaseous fuels, they can be stored relatively easily and the amount of energy that can be contained in the vehicle fuel tank is relatively high (although still less than when using gasoline).

The work reports results from tests employing different cooled EGR routes on a ‘Sabre’ direct-injection spark-ignition (DISI) research engine. As standard, this engine has been configured to provide good fuel consumption from a combination of mild downsizing, a combustion system with close-spaced injection and the adoption of a three-cylinder configuration in concert with an exhaust manifold integrated into the cylinder head. This has already been shown to offer a rated power specific fuel consumption of 272 g/kWh without cooled EGR. Three different EGR configurations are tested, with the best BSFC at nominal rated conditions being found to be 257-258 g/kWh at a cooled EGR rate of 6%. All of the EGR routing configurations tested in this work permit ready operation of the engine at Lambda 1 and MBT conditions, however, the results show little sensitivity in the combustion system to the actual routing employed.

Many new technologies are being developed to improve the fuel consumption of gasoline engines, including the combination of direct fuel injection with turbocharging in a so-called ‘downsizing’ approach. In such spark ignition engines operating on the Otto cycle, downsizing targets a shift in the operating map such that the engine is dethrottled to a greater extent during normal operation, thus reducing pumping losses and improving fuel consumption. However, even with direct injection, the need for turbine protection fuelling at high load in turbocharged engines - which is important for customer usage on faster European highways such as German Autobahns - brings a fuel consumption penalty over a naturally-aspirated engine in this mode of operation.

Concerns over energy security and global warming are beginning to be a serious issue for society and are also starting to drive customer purchasing decisions across many areas. Against this background there is an increasing call for motor sport to improve its environmental image, despite the fact that the global energy consumption and CO2 emissions attributable to motor sport are a very low proportion of the total. The real issue for motor sport in the face of the wider societal concerns is that, if it is truly at the cutting edge of relevant automotive engineering, it should be configured and managed in such a way as to drive technology for the betterment of mankind. The status quo is, it is contended, increasingly seen to be blatantly energy-profligate in the eyes of many people and this issue must be resolved if motor sport is to demonstrate the wider benefits of the technology developed by the huge financial investments committed to competing at the highest level.

The paper critiques proposals for de-carbonizing transport and offers a potential solution which may be attained by the gradual evolution of the current fleet of predominantly low-cost vehicles via the development of carbon-neutral liquid fuels. The closed-carbon cycles which are possible using such fuels offer the prospect of maintaining current levels of mobility with affordable transport whilst neutralizing the threat posed by the high predicted growth of greenhouse gas emissions from this sector. Approaches to de-carbonizing transport include electrification and the adoption of molecular hydrogen as an energy carrier. These two solutions result in very expensive vehicles for personal transport which mostly lie idle for 95% of their life time and are purchased with high-cost capital.

Electrohydraulic and electromechanical valve train technologies for four-stroke engines are emerging which allow much greater flexibility and control of the valve events than can be achieved using mechanically-based systems. Much of the work done on exploiting the benefits of these systems has been directed towards improving engine fuel economy and reducing emissions. In the present work a study has been made, using an engine simulation program, in to some of the possible benefits to engine performance that may be facilitated by the flexibility of fully variable valve train (FVVT) systems. The simulation study indicates that FVVT systems, limited by realistic opening and closing rates, provide sufficient range in the valve event duration and timing to enable the engine to produce very high specific outputs whilst achieving a high level of torque in the low- and mid-speed range.

An expedient route to improving in-vehicle fuel economy in 4-stroke cycle engines is to reduce the swept volume of an engine and run it at a higher BMEP for any given output. The full-load performance of a larger capacity engine can be achieved through pressure charging. However, for maximum fuel economy, particularly at part-load, the expansion ratio, and consequently the compression ratio (CR) should be kept as high as possible. This is at odds with the requirement in pressure-charged gasoline engines to reduce the CR at higher loads due to the knock limit. In earlier work, the authors studied a pressure-charging system aimed at allowing a high CR to be maintained at all times. The operation of this type of system involves deliberately over-compressing the charge air, cooling it at the elevated pressure and temperature, and then expanding it down to the desired plenum pressure, ensuring a plenum temperature which can potentially become sub-atmospheric at full-load.