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Development of new fuels and engine combustion strategies for future ultra-low emission engines requires a greater level of insight into the process of emissions formation than is afforded by the approach of engine exhaust measurement. The paper describes the development of an in-cylinder gas sampling system consisting of a fast-acting, percussion-based, poppet-type sampling valve, and a heated dilution tunnel; and the deployment of the system in a single cylinder engine. A control system was also developed for the sampling valve to allow gas samples to be extracted from the engine cylinder during combustion, at any desired crank angle in the engine cycle, while the valve motion was continuously monitored using a proximity sensor. The gas sampling system was utilised on a direct injection diesel engine co-combusting a range of hydrogen-diesel fuel and methane-diesel fuel mixtures.

This paper addresses the need for fundamental understanding of the mechanisms of fuel spray formation and mixture preparation in direct injection spark ignition (DISI) engines. Fuel injection systems for DISI engines undergo rapid developments in their design and performance, therefore, their spray breakup mechanisms in the physical conditions encountered in DISI engines over a range of operating conditions and injection strategies require continuous attention. In this context, there are sparse data in the literature on spray formation differences between conventionally drilled injectors by spark erosion and latest Laser-drilled injector nozzles. A comparison was first carried out between the holes of spark-eroded and Laser-drilled injectors of same nominal type by analysing their in-nozzle geometry and surface roughness under an electron microscope.

Improvements in the efficiency of internal combustion engines and the development of renewable liquid fuels have both been deployed to reduce exhaust emissions of CO2. An additional approach is to scrub CO2 from the combustion gases, and one potential means by which this might be achieved is the reaction of combustions gases with sodium borohydride to form sodium carbonate. This paper presents experimental studies carried out on a modern direct injection diesel engine supplied with a solution of dissolved sodium borohydride so as to investigate the effects of sodium borohydride on combustion and emissions. Sodium borohydride was dissolved in the ether diglyme at concentrations of 0.1 and 2 % (wt/wt), and tested alongside pure diglyme and a reference fossil diesel. The sodium borohydride solutions and pure diglyme were supplied to the fuel injector under an inert atmosphere and tested at a constant injection timing and constant engine indicated mean effective pressure (IMEP).

This paper presents a study of the combustion mechanism of hydrous and anhydrous ethanol in comparison to iso-octane and gasoline fuels in a single-cylinder spark-ignition research engine operated at 1000 rpm with 0.5 bar intake plenum pressure. The engine was equipped with optical access and tests were conducted with both Port Fuel Injection (PFI) and Direct Injection (DI) mixture preparation methods; all tests were conducted at stoichiometric conditions. The results showed that all alcohol fuels, both hydrous and anhydrous, burned faster than iso-octane and gasoline for both PFI and DI operation. The rate of combustion and peak cylinder pressure decreased with water content in ethanol for both modes of mixture preparation. Flame growth data were obtained by high-speed chemiluminescence imaging. These showed similar trends to the mass fraction burned curves obtained by in-cylinder heat release analysis for PFI operation; however, the trend with DI was not as consistent as with PFI.

International obligations to reduce carbon dioxide emissions and requirements to strengthen security of fuel supply, indicate a need to diversify towards the use of cleaner and more sustainable fuels. Hydrogen has been recommended as an encouraging gaseous fuel for future road transportation since with reasonable modifications it can be burned in conventional internal combustion engines without producing carbon-based tailpipe emissions. Direct injection of hydrogen into the combustion chamber can be more preferable than port fuel injection since it offers advantages of higher volumetric efficiency and can eliminate abnormal combustion phenomena such as backfiring. The current work applied a fully implicit computational methodology along with the Reynolds-Averaged Navier-Stokes (RANS) approach to study the mixture formation and combustion in a direct-injection spark-ignition engine with hydrogen fuelling.

Iso-stoichiometric ternary blends - in which three-component blends of gasoline, ethanol and methanol are configured to the same stoichiometric air-fuel ratio as an equivalent binary ethanol-gasoline blend - can function as invisible "drop-in" fuels suitable for the existing E85/gasoline flex-fuel vehicle fleet. This has been demonstrated for the two principal means of detecting alcohol content in such vehicles, which are considered to be a virtual, or software-based, sensor, and a physical sensor in the fuel line. Furthermore when using such fuels the tailpipe CO₂ emissions are essentially identical to those found when the vehicle is operated on E85. Because of the fact that methanol can be made from a wider range of feed stocks than ethanol and at a cheaper price, these blends then provide opportunities to improve energy security, to reduce greenhouse gas emissions and to produce a fuel blend which could potentially be cheaper on a cost-per-unit-energy basis than gasoline or diesel.

Five different fuels, including gasoline, commercial E85, pure methanol and two mixtures of gasoline, ethanol and methanol, (GEM), configured to a target stoichiometric air fuel ratio have been investigated in a fully-optically-accessed engine. The work investigated effects of injection duration, and performed spray imaging, thermodynamic analysis of the combustion and OH imaging, for two fixed engine conditions of 2.7 and 3.7 bar NMEP at 2000 rpm. The engine was operated with constant ignition timing for all fuels and both loads. One of the most important results from this study was the suitability of a single type of injector to handle all the fuels tested. There were differences observed in the spray morphology between the fuels, due to the different physical properties of the fuels. The energy utilisation measured in this study showed differences of up to 14% for the different GEM fuels whereas an earlier in-vehicle study had showed only 2 to 3%.

The fuel economy and emissions performance of a Diesel engine is strongly influenced by the fuel injection process. This paper presents early results of an experimental investigation into diesel spray development carried out in a novel in-house developed optical pressure chamber capable of operating at pressure up to 50 bar and temperatures up to 900 K. The spatial evolution of a diesel spray tends to experience many transitory macroscopic phenomena that directly influence the mixing process. These phenomena are not considered highly reproducible and are extremely short lived, hence recording and understanding these transient effects is difficult. In this study, high-speed backlight-illuminated imaging has been employed in order to capture the transient dynamics of a short signal duration diesel spray injected into incremental back pressures and temperatures reaching a maximum of 10 bar and 473 K respectively.

The Swedish Biomimetics 3000's μMist® platform technology has been used to develop a radically new injection system. This prototype system, developed and characterized with support from Lotus, as part of Swedish Biomimetics 3000®'s V₂IO innovation accelerating model, delivers improved combustion efficiency through achieving exceptionally small droplets, at fuel rail pressures far less than conventional GDI systems and as low as PFI systems. The system gives the opportunity to prepare and deliver all of the fuel load for the engine while the intake valves are open and after the exhaust valves have closed, thereby offering the potential to use advanced charge scavenging techniques in PFI engines which have hitherto been restricted to direct-injection engines, and at a lower system cost than a GDI injection system.

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.

This experimental work was concerned with the combination of internal EGR with an early inlet valve closure strategy for improved part-load fuel economy. The experiments were performed in a new spark-ignited thermodynamic single cylinder research engine, equipped with a mechanical fully variable valvetrain on both the inlet and exhaust. During unthrottled operation at constant engine speed and load, increasing the mass of trapped residual allowed increased valve duration and lift to be used. In turn, this enabled further small improvements in gas exchange efficiency, thermal efficiency and hence indicated fuel consumption. Such effects were quantified under both port and homogeneous central direct fuel injection conditions. Shrouding of the inlet ports as a potential method to increase in-cylinder gas velocities has also been considered.

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.

Biodiesel is a renewable fuel which can be used as a direct replacement for fossil Diesel fuel as a calorific source in Diesel Engines. It consists of fatty acid mono-alkyl esters, which are produced by the trans-esterification reaction of plant oils with monohydric alcohols. The Plant oils and alcohols can both be derived from biomass, giving this fuel the potential for a sustainable carbon dioxide neutral life-cycle, which is an important quality with regard to avoiding the net emission of anthropogenic greenhouse gases. Depending on its fatty ester composition, Biodiesel can have varying physical and chemical properties which influence its combustion behaviour in a Diesel engine. It has been observed by many researchers that Biodiesel can sometimes lead to an increase in emissions of oxides of nitrogen (NOx) compared to fossil Diesel fuel, while emitting a lower amount of particulate mass.

For a spark-ignition engine, the parasitic loss suffered as a result of conventional throttling has long been recognised as a major reason for poor part-load fuel efficiency. While lean, stratified charge, operation addresses this issue, exhaust gas aftertreatment is more challenging compared with homogeneous operation and three-way catalyst after-treatment. This paper adopts a different approach: homogeneous charge direct injection (DI) operation with variable valve actuations which reduce throttling losses. In particular, low-lift and early inlet valve closing (EIVC) strategies are investigated. Results from a thermodynamic single cylinder engine are presented that quantify the effect of two low-lift camshafts and one standard high-lift camshaft operating EIVC strategies at four engine running conditions; both, two- and single-inlet valve operation were investigated. Tests were conducted for both port and DI fuelling, under stoichiometric conditions.

Synthetic bio-fuels, which can be obtained through the gasification of biomass into synthesis gas and the subsequent catalytic reaction of the synthesis gas into liquid fuel molecules, could play a key-role in providing a sustainable source of automotive fuels during the coming decades. This paper presents an attempt to understand the effect of molecular structure of potential oxygenated synthetic bio-fuel molecules of different structure on the diesel combustion process in both stratified and homogeneous combustion modes. Specifically, the effects of molecular structure on the energy release rates, gaseous exhaust emissions and the sub-micron particulate matter distribution were examined. The experiments were carried out on a single-cylinder direct-injection diesel engine using a specially adapted common-rail fuel-system which allowed the injection of small single-molecule fuel samples at high pressure.

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 effect on the intake flow field, air fuel mixing processes, thermodynamic performance and emissions output has been investigated for a range of valve operating profiles. A standard speed load point of 2000 rpm and 2.7 bar IMEP720° has been reached by throttling the intake whilst running standard cam profiles, by early closing of both inlet valves (EIVC) and by early closing of each inlet individually to generate bulk swirl motions within the cylinder. Data has been recorded at stoichiometric air fuel ratios for both direct injection and port fuelled operation. The valve profiles have been applied to two single cylinder homogeneous gasoline direct injection (GDI) spark ignition engines, developed to investigate the potential of controlling engine load by limiting the inducted air mass using fully variable valve timing (FVVT) to reduce pumping losses at part load.

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 effects of impinging airflow on the near nozzle characteristics of an inwardly opening, high pressure-swirl atomiser are investigated in an optically-accessed, steady-state flow rig designed to emulate the intake flow of a typical, side-injected, 4-valve gasoline direct-injection combustion system. The results indicate that the impinging airflow has a relatively minor effect on the initial break-up of the fuel spray. However, the secondary break-up of the spray, i.e. the break-up of liquid ligaments, the spatial distribution of droplets within the spray and the location of the spray within the cylinder are significantly affected by the impinging air.

Homogenous Charge Compression Ignition (HCCI) is an alternative to Spark Ignited (SI) combustion, which can provide part-load efficiencies as high as compression ignition engines and energy densities as high as SI engines, without high levels of NOx or Particulate Matter (PM). The principle of operation involves reaching the thermal oxidization barrier of a homogeneous air-fuel mixture. This combustion practice is enabled by diluting then compressing the mixture with the Trapped Residual Gases (TRG) to dilute the initial charge thus keeping combustion temperatures down. Introduction of exhaust gasses in the mixture can be achieved by the use of early exhaust valve closure and late inlet valve opening. The charge is well mixed avoiding particulate emissions, and by using exhaust gasses for load regulation the need for throttled operation is removed allowing the realization of high efficiencies, low pumping losses and a resulting 15 - 20% improvement in fuel economy.