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Modern diesel passenger car technology continues to develop rapidly in response to demanding emissions, performance, refinement, cost and fuel efficiency requirements. This has included the implementation of high pressure common rail fuel systems employing high precision injectors with complex injection strategies, higher hydraulic efficiency injector nozzles and in some cases <100µm nozzle hole diameters. With the trend towards lower diameter diesel injector nozzle holes and reduced cleaning through cavitation with higher hydraulic efficiency nozzles, it is increasingly important to focus on understanding the mechanism of diesel injector nozzle deposit formation and growth. In this study such deposits were analysed by cross-sectioning the diesel injector along the length of the nozzle hole enabling in-depth analysis of deposit morphology and composition change from the inlet to the outlet, using state-of-the-art electron microscopy techniques.

The accurate confirmation of fuel economy benefits arising from the use of a gasoline additive package is a difficult exercise. In order to fully understand, and accurately quantify, the interaction between the treated fuel and the engine it is necessary to carry out a fleet test which allows the benefit to be measured precisely yet under realistic conditions. A series of road tests, based on a ‘paired fleet’ design, has been carried out over the last two decades. Careful analysis of the results of these tests has led to the design of a new fleet testing protocol based around ‘quads’ rather than pairs of vehicles. This new test protocol also incorporates advances in vehicle selection and preparation procedures and has resulted in a test that is both more robust and flexible, and that achieves even better resolution than before.

The octane appetite of an SI engine can be expressed in terms of an Octane Index: OI = (1−K) RON + K MON where K is a constant for a given operating condition and depends only on the pressure and temperature variation in the engine (it is not a property of the fuel). Experimental measurements of K values can be costly and time consuming. This paper reports the development of a new K-value simulation method that can be applied to any spark ignition engine given basic engine data. Good agreement between simulation and experimental results suggests the method is reliable and can be applied to a wide range of engines.

Improved fuel economy is increasingly a key measure of performance in the automotive industry driven by market demands and tighter emissions regulations. Within this environment, one way to improve fuel economy is via fuel additives that deliver friction- reducing components to the piston-cylinder wall interface. Whilst the use of friction modifiers (FMs) in fuel or lubricant additives to achieve fuel economy improvements is not new, demonstrating the efficacy of these FMs in vehicles is challenging and requires statistical design together with carefully controlled test conditions. This paper describes a bespoke, efficient, high-precision vehicle testing procedure designed to evaluate the fuel economy credentials of fuel-borne FMs. By their nature, FMs persist on engine surfaces and so their effects are not immediately reversible upon changing to a non FM-containing fuel (“carryover” effect), therefore requiring careful design of the test programme.

Precise, repeatable and representative testing is a key tool for developing and demonstrating automotive fuel and lubricant products. This paper reports on the first findings of a project that aims to determine the requirements for highly repeatable test methods to measure very small differences in fuel economy and powertrain performance. This will be underpinned by identifying and quantifying the variations inherent to this specific test vehicle, both on-road and on Chassis Dynamometer (CD), that create a barrier to improved testing methods. In this initial work, a comparison was made between on-road driving, the New European Drive Cycle (NEDC) and World harmonized Light-duty Test Cycle (WLTC) cycles to understand the behavior of various vehicle systems along with the discrepancies that can arise owing to the particular conditions of the standard test cycles.

A series of viscous and surface friction modifier additives has been studied in a modified SI engine with separable valve train lubrication. From the results, it has been possible to classify the hydrodynamic or boundary lubrication nature of the observed effects for a series of lubricant additives. It is shown that the frictional benefit of a given additive depends not only on the engine operating condition but also on the engine components on which it is acting. For some additives a fuel economy benefit can switch to a disbenefit as operating regime changes and a different aspect of the additive properties becomes important. Such observations are rationalised in the context of conventional lubrication theory.

Downsized turbocharged gasoline direct injection (TGDI) engines with high specific power and torque can enable reduced fuel consumption in passenger vehicles while maintaining or even improving on the performance of larger naturally aspirated engines. However, high specific torque levels, especially at low speeds, can lead to abnormal combustion phenomena such as knock or Low-Speed Pre-Ignition (LSPI). LSPI, in particular, can limit further downsizing due to resulting and potentially damaging mega-knock events. Herein, we characterize the impacts of lubricant and fuel composition on LSPI frequency in a TGDI engine while specifically exploring the correlation between fuel composition, particulate emissions, and LSPI events. Our research shows that: (1) oil composition has a strong impact on LSPI frequency and that LSPI frequency can be reduced through a carefully focused approach to lubricant formulation.

Carbonaceous deposits can accumulate on various surfaces of the internal combustion engine and affect its performance. The porous nature of these deposits means that they act like a “sponge”, adsorbing fuel components and changing both the composition and the amount of fuel in the combustion chamber. Here we use a previously developed and validated model of engine deposits to predict adsorption of normal heptane, isooctane, toluene and their mixtures in deposits of different origin within a port fuel injected spark ignition engine (Combustion Chamber Deposits, or CCDs, and Intake Valve Deposits, or IVDs) and under different conditions. We explore the influence of molecular structure of adsorbing species, composition of the bulk mixture and temperature on the uptake and selectivity behaviour of the deposits. While deposits generally show high capacity toward all three components, we observe that selectivity behaviour is a more subtle and complex property.

Exhaust Gas Recirculation (EGR) is employed in diesel engines to reduce engine-out NOx emissions. Despite the concerted design efforts of manufacturers, high-pressure Exhaust Gas Recirculation (HP-EGR) systems can be susceptible to fouling as the particulate matter, hydrocarbons and other entrained species deposit from the exhaust gas flow as it cools on its passage through the EGR system. Such deposits can lead to a number of problems including deterioration of emissions, fuel efficiency, performance and drivability, as well as breakdowns. The development of an engine test method to enable the study of the impact of fuel on deposits in the HP-EGR system was reported in 2020. In the test, a 4-cylinder light-duty diesel engine of 1.6L displacement runs at conditions conducive to EGR deposit formation over 24 hours and the impact of fuels on deposit formation is determined through weighing of the EGR system components before and after the test.

Because reformer technology can be used in conjunction with advanced internal combustion engine technology, it is important to be able to formulate fuels that are compatible with both reformers and ICEs It has been found that most hydrocarbon species typically present in gasoline can be reformed with relative ease. The exception is that olefinic species of carbon number 6 and above are relatively much harder to reform. It is shown how a reformer compatible gasoline fuel with high octane can be blended. For Diesel fuels, synthetic ‘Gas to Liquid’ fuels are generally less susceptible to coking and hence superior to petroleum-derived fuels, for use with an onboard reformer.

Design efforts to improve the hydraulic efficiency of high-pressure diesel fuel systems and thus further improve overall engine efficiency have resulted in the utilisation of low-spill control valves and reduced injector component clearances to reduce general leakage losses. Overall, these advances have contributed significantly to the high efficiency diesel engines of today. However, the combination of very high fuel pressures, cavitation and low fuel leakage volumes increases the heating of the remaining fuel, increasing temperature and, in turn, the propensity for deposits to form inside the injector. This deposit phenomenon is commonly known as Internal Diesel Injector Deposits (IDID) and can cause rough engine running and failed engine starts requiring injector cleaning or replacement. Methods studying this phenomenon are under development in the industry.

Driven by increasingly stringent tailpipe CO2 and fuel economy regulations, gasoline direct injection (GDI) engines are enjoying rapidly increasing market penetration. Already more than 50% of newly produced vehicles in the US and western Europe employ direct-injection technology and many markets in Asia are also seeing an increasingly rapid uptake. However, with the adoption of GDI engine technology, which is able to push the boundaries of engine efficiency, new challenges are starting to arise such as injector nozzle deposits, which can adversely affect performance. Multi-hole solenoid actuated fuel injectors are particularly vulnerable to deposits formed when operated on some market fuels. In order to address this challenge, the development of a reliable industry test platform for injector cleanliness in GDI engines is currently underway in both the US and Europe.

Exhaust Gas Recirculation (EGR) is employed in diesel engines to reduce engine-out NOx. Carbon-containing deposits form in the EGR systems of modern diesel engines as the particulate matter, hydrocarbons and other entrained species deposit from the exhaust gas flow as it cools. Much work has been done by Original Equipment Manufacturers (OEMs) to reduce deposits and mitigate their effects by optimized dimensioning of EGR coolers and valves, introduction of EGR cooler bypass for use in the most sensitive cold conditions and experimenting with oxidation catalysts upstream of the EGR system. Nevertheless, deposits forming in the high-pressure Exhaust Gas Recirculation (HP-EGR) systems of modern diesel engines can sometimes lead to a number of problems including emissions and fuel consumption deterioration, poor performance and drivability, as well as breakdowns. An engine test method has been developed to enable the impact of fuel on deposits in the HP-EGR system to be studied.

Reduction of vehicle exhaust emissions is an important contributor to improved air quality. At the same time demand is growing for new transportation fuels that can enhance security and diversity of energy supply. Gas to Liquids (GTL) Fuel has generated much interest from governments and automotive manufacturers. It is a liquid fuel derived from natural gas, and its properties - sulphur free, low polyaromatics and high cetane number - make it desirable for future clean light-duty diesel engines. In this paper, the effects of distillation characteristics and cetane number of experimental GTL test fuels on direct injection (DI) diesel combustion and exhaust emissions were investigated, together with their spray behaviour and mixing characteristics. The test results show that the lower distillation test fuels produce the largest reductions in smoke and PM emissions even at high cetane numbers. This is linked to the enhanced air/fuel mixing of the lighter fuel in a shorter time.

It is useful for research purposes to define simple surrogate gasoline compositions that can replicate the chemical and physical properties of more complex mixtures. Ethanol is used in commercially available gasolines around the world as part of the pathway to the decarbonization of the transportation sector. In this study equations were developed to predict the Research Octane Number (RON), Motor Octane Number (MON) and Dry Vapour Pressure Equivalent (DVPE) of gasoline surrogates containing ethanol (10-25 vol%), isopentane, n-heptane, isooctane and toluene. The non-linear blending behaviour associated with ethanol is found to necessitate coefficients in the equations developed for MON that are a function of ethanol content, whereas surprisingly the equations for RON and DVPE do not need this added level of complexity.

It is anticipated that worldwide energy demand will approximately double by 2050, whilst at the same time, CO2 emissions need to be halved. Therefore, there is increasing pressure to improve the efficiency of all machines, with great focus on improving the fuel efficiency of passenger cars. The use of downsized, boosted, gasoline engines, can lead to exceptional fuel economy, and on a well-to-wheels basis, can give similar CO2 emissions to electric vehicles (depending, of course, on how the electricity is generated). In this paper, the development of a low weight concept car is reported. The car is equipped with a three-cylinder 0.66 litre gasoline engine, and has achieved over 100 miles per imperial gallon, in real world driving conditions.

Demonstrating the cost/benefits of technologies in the automotive sector is becoming very challenging because the benefits from technologies are sometimes of similar magnitude to testing precision. This paper aims to understand vehicle-borne imprecision and the effect of this on the quality of chassis dynamometer (CD) testing. Fuel consumption and NOx emissions precision is analyzed for two diesel vehicles with particulate filter and SCR systems. The two vehicles were tested on a high precision CD facility over the NEDC (New European Drive Cycle) and WLTC (World harmonized Light-duty Test Cycle) cycles. The CD base precision of testing was characterized between 0.6-3% depending on the cycle phase. A novel application of multi-variate statistical analysis was used to identify the factors that affected testing precision, allowing isolation of small differences that were not obvious when conducting cycle-averaged or cycle-phase-averaged analysis.

Deposits forming in the injector nozzle holes of modern diesel cars can reduce and disrupt the fuel injected into the combustion chamber, causing reduced or less efficient combustion, resulting in power loss and increased fuel consumption. A study of the factors affecting injector nozzle tip temperature, a parameter critical to nozzle deposit formation, has been conducted in a Peugeot DW10 passenger car bench engine, as used in the industry standard CEC F-098 injector nozzle deposit test, [1]. The findings of the bench engine study were applied in the development of a Chassis Dynamometer (CD) based vehicle test method using Euro 5 compliant vehicles. The developed test method was refined to tune the conditions as far as practicable towards a realistic driving pattern whilst maintaining sufficient deposit forming tendency to enable test duration to be limited to a reasonable period.

Due to the recent drive to reduce CO₂ emissions, the turbocharged direct injection spark ignition (turbo DISI) gasoline engine has become increasingly popular. In addition, future turbo DISI engines could incorporate a form of charge dilution (e.g., lean operation or external EGR) to further increase fuel efficiency. Thus, the conditions experienced by the fuel before and during combustion are and will continue to be different from those experienced in naturally aspirated SI engines. This work investigates the effects of fuel properties on a modern and prototype turbo DISI engine, with particular focus on the octane appetite: How relevant are RON and MON in predicting a fuel's anti-knock performance in these modern/future engines? It is found that fuels with high RON and low MON values perform the best, suggesting the current MON requirements in fuel specifications could actually be detrimental.

The introduction of sulphur-free fuels will enable advanced engine and exhaust after-treatment technologies to meet increasingly stringent exhaust emissions regulations. As these cleaner fuels and vehicles are introduced, the potential for further improvements in air quality through changes to fuel properties can be expected to diminish. Nevertheless, CONCAWE has continued to update knowledge by evaluating fuel effects on emissions from new engine/vehicle technologies as they approach the market. In this work, carried out as part of CONCAWE's contribution to the EU “PARTICULATES” consortium [1], two advanced light-duty diesel vehicles and three heavy-duty diesel engines covering Euro-3 to Euro-5 technologies, were tested. The fuels tested covered a range of sulphur content and compared conventional fuels with extreme fuel compositions such as Swedish Class 1 and Fischer Tropsch diesel fuels.