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Injector nozzle deposits can have a profound effect on particulate emissions from vehicles fitted with Gasoline Direct Injection (GDI) engines. Several recent publications acknowledge the benefits of using Deposit Control Additives (DCA) to maintain or restore injector cleanliness and in turn minimise particulates, but others claim that high levels of DCA could have detrimental effects due to the direct contribution of DCA to particulates, that outweigh the benefits of injector cleanliness. Much of the aforementioned work was conducted in laboratory scenarios with model fuels. In this investigation a fleet of 7 used GDI vehicles were taken from the field to determine the net impact of DCAs on particulates in real-world scenarios. The vehicles tested comprised a range of vehicles from different manufacturers that were certified to Euro 5 and Euro 6 emissions standards.

Injector fouling is an important contributory factor to particulate matter (PM) emissions in Gasoline Direct Injection (GDI) engines. Several publications have emerged in recent years which acknowledge the benefits of injector cleanliness, but others claim that high levels of Deposit Control Additive (DCA) could have detrimental effects that outweigh the benefits of the augmented cleaning potential. The paper is divided into two parts: The first part contains a critical review of the literature linking injector cleanliness and particulate matter emissions, and studies assessing the impact of higher treat rates of additives. The second part of the paper describes new evidence of the beneficial effects of DCAs, in the form of several separate (previously unpublished) studies, using both engines and vehicles. In this newly reported work, various DCA treat rates were employed, and some of the fuels had measured UWG levels well in excess of 50 mg/100 mL.

In the present study, Large Eddy Simulations (LES) have been performed with a 3D model of a step nozzle injector, using n-pentane as the injected fluid, a representative of the high-volatility components in gasoline. The influence of fuel temperature and injection pressure were investigated in conditions that shed light on engine cold-start, a phenomenon prevalent in a number of combustion applications, albeit not extensively studied. The test cases provide an impression of the in-nozzle phase change and the near-nozzle spray structure across different cavitation regimes. Results for the 20oC fuel temperature case (supercavitating regime) depict the formation of a continuous cavitation region that extends to the nozzle outlet. Collapse-induced pressure wave dynamics near the outlet cause a transient entrainment of air from the discharge chamber towards the nozzle.

Blends of gasoline, diesel fuel and ethanol (“dieseline”) have shown promise in engine studies examining low temperature combustion using compression ignition. They offer the possibility of high efficiency combined with low emissions of oxides of nitrogen and soot. However, unlike gasoline or diesel fuel alone, such mixtures can be flammable in the headspace above the liquid in a vehicle fuel tank at common ambient temperatures. Quantifying their flammability characteristics is important if these fuels are to see commercial service. The parameter of most interest is the Upper Flammable Limit (UFL) temperature, below which the headspace vapour is flammable. In earlier work a mathematical model to predict the flammability of dieseline blends, including those containing ethanol, was developed and validated experimentally. It was then used to study the flammability of a wide variety of dieseline blends parametrically.

A practical Gasoline Compression Ignition (GCI) concept is presented that works on standard European 95 RON E10 gasoline over the whole speed/load range. A spark is employed to assist the gasoline autoignition at low loads; this avoids the requirement of a complex cam profile to control the local mixture temperature for reliable autoignition. The combustion phasing is controlled by the injection pattern and timing, and a sufficient degree of stratification is needed to control the maximum rate of pressure rise and prevent knock. With active control of the swirl level, the combustion system is found to be relatively robust against variability in charge motion, and subtle differences in fuel reactivity. Results show that the new concept can achieve very low fuel consumption over a significant portion of the speed/load map, equivalent to diesel efficiency. The efficiency is worse than an equivalent diesel engine only at low load where the combustion assistance operates.

The octane appetite of an engine is frequently characterised by the so-called K value. It is usually assumed that K is dependent only on the thermodynamic conditions in the engine when knock occurs. In this work we test this hypothesis: further analysis was conducted on experimental results from SAE 2019-01-0035 in which a matrix of fuels was tested in a single cylinder engine. The fuels consisted of a relatively small number of components, thereby simplifying the analysis of the chemical kinetic proprieties. Through dividing the original fuel matrix into subsets, it was possible to explore the variation of K value with fuel properties. It was found that K value tends to increase slightly with RON. The explanation for this finding is that higher RON leads to advanced ignition timing (i.e. closer to MBT conditions) and advanced ignition timing results in faster combustion because of the higher pressures and temperatures reached in the thermodynamic trajectory.

Low Temperature Combustion using compression ignition may provide high efficiency combined with low emissions of oxides of nitrogen and soot. This process is facilitated by fuels with lower cetane number than standard diesel fuel. Mixtures of gasoline and diesel (“dieseline”) may be one way of achieving this; however, a gasoline/diesel mixture in a fuel tank can result in a flammable headspace, particularly at very cold ambient temperatures. A mathematical model to predict the flammability of dieseline blends, including those containing ethanol, was previously validated. In this paper, that model is used to study the flammability of dieseline blends parametrically. Gasolines used in the simulations had Dry Vapour Pressure Equivalent (DVPE) values of 45, 60, 75, 90 and 110 kPa.

In recent years, boosted and downsized engines have gained much attention as a promising technology to improve fuel economy; however, knocking is a common issue of such engines that requires attention. To understand the knocking phenomenon under downsized and boosted engine conditions deeply, fuels with different Research Octane Number (RON) and Motor Octane Number (MON) were prepared, and the knocking performances of these fuels were evaluated using a single cylinder engine, operated under a variety of conditions. Experimental results showed that the knocking performance at boosted conditions depend on both RON and MON. While higher RON showed better anti-knocking performance, lower MON showed better anti-knocking performance. Furthermore, the tendency for a reduced MON to be beneficial became stronger at lower engine speeds and higher boost pressures, in agreement with previously published modelling work.

The accepted model of conventional diesel combustion [1] assumes a rich premixed flame slightly downstream of the maximum liquid penetration. The soot generated by this rich premixed flame is burnt out by a subsequent diffusion flame at the head of the jet. Even in situations in which the centre of combustion (CA50) is phased optimally to maximize efficiency, slow late stage combustion can still have a significant detrimental impact on thermal efficiency. Data is presented on potential late-stage combustion improvers in a EURO VI compliant HD engine at a range of speed and load points. The operating conditions (e.g. injection timings, EGR levels) were based on a EURO VI calibration which targets 3 g/kWh of engine-out NOx. Rates of heat release were determined from the pressure sensor data. To investigate late stage combustion, focus was made on the position in the cycle at which 90% of the fuel had combusted (CA90). An EN590 compliant fuel was tested.

Stringent regulations on fuel economy have driven major innovative changes in the internal combustion engine design. (E.g. CAFE fuel economy standards of 54.5 mpg by 2025 in the U.S) Vehicle manufacturers have implemented engine infrastructure changes such as downsizing, direct injection, higher compression ratios and turbo-charging/super-charging to achieve higher engine efficiencies. Fuel properties therefore, have to align with these engine changes in order to fully exploit the possible benefits. Fuel octane number is a key metric that enables high fuel efficiency in an engine. Greater resistance to auto-ignition (knock) of the fuel/air mixture allows engines to be operated at a higher compression ratio for a given quantity of intake charge without severely retarding the spark timing resulting in a greater torque per mass of fuel burnt. This attribute makes a high octane fuel a favorable hydrocarbon choice for modern high efficiency engines that aim for higher fuel economy.

Port fuel injected (PFI) technology remains the most common fuel delivery type present in the marketplace for gasoline spark ignition engines and a legacy vehicle fleet featuring PFI technology will remain in the market for decades to come. This is especially the case in parts of Asia where PFI technology is still prominent, although direct injection (DI) technology adoption is starting to catch up. PFI engines can, when operated with lower quality fuels and lubricants, build up performance impairing deposits on a range of critical engine parts including in the fuel injectors, combustion chamber and on inlet valves. Inlet valve deposits (IVDs) in more severe cases have been associated with drivability issues such as engine stumble and engine hesitation on sudden acceleration. Deposit control additives in gasoline formulations are a well-established route to managing and even reversing fuel system fouling.

Low Temperature Combustion using compression ignition may provide high efficiency combined with low emissions of oxides of nitrogen and soot. This process is facilitated by fuels with lower cetane number than standard diesel fuel. Mixtures of gasoline and diesel (“dieseline”) may be one way of achieving this, but a practical concern is the flammability of the headspace vapours in the vehicle fuel tank. Gasoline is much more volatile than diesel so, at most ambient temperatures, the headspace vapours in the tank are too rich to burn. A gasoline/diesel mixture in a fuel tank therefore can result in a flammable headspace, particularly at cold ambient temperatures. A mathematical model is presented that predicts the flammability of the headspace vapours in a tank containing mixtures of gasoline and diesel fuel. Fourteen hydrocarbons and ethanol represent the volatile components. Heavier components are treated as non-volatile diluents in the liquid phase.

In Gasoline Direct Injection engines, direct exposure of the injector to the flame can cause combustion products to accumulate on the nozzle, which can result in increased particulate emissions. This research observes the impact of injector fouling on particulate emissions and the associated injector spray pattern and shows how both can be reversed by utilising fuel detergency. For this purpose multi-hole injectors were deliberately fouled in a four-cylinder test engine with two different base fuels. During a four hour injector fouling cycle particulate numbers (PN) increased by up to two orders of magnitude. The drift could be reversed by switching to a fuel blend that contained a detergent additive. In addition, it was possible to completely avoid any PN increase, when the detergent containing fuel was used from the beginning of the test. Microscopy showed that increased injector fouling coincided with increased particulate emissions.

In light of increasingly stringent CO2 emission targets, Original Equipment Manufacturers (OEM) have been driven to develop engines which deliver improved combustion efficiency and reduce energy losses. In spark ignition engines one strategy which can be used to reach this goal is the full utilization of fuel octane number. Octane number is the fuel´s knock resistance and is characterized as research octane number (RON) and motor octane number (MON). Engine knock is caused by the undesired self-ignition of the fuel air mixture ahead of the flame front initiated by the spark. It leads to pressure fluctuations that can severely damage the engine. Modern vehicles utilize different strategies to avoid knock. One extreme strategy assumes a weak fuel quality and, to protect the engine, retards the spark timing at the expense of combustion efficiency. The other extreme carefully detects knock in every engine cycle and retards the spark timing only when knock is detected.

Modern spark ignition engines can take advantage of better fuel octane quality either towards improving acceleration performance or fuel economy via an active ignition management system. Higher fuel octane allows for spark timing advance and consequently higher torque output and higher engine efficiency. Additionally, engines can be designed with higher compression ratios if a higher anti-knock quality fuel is used. Due to historical reasons, Research Octane (RON) and Motor Octane Number (MON) are the metrics used to characterize the anti-knock quality of a fuel. The test conditions used to compute RON and MON correlated well with those in older engines designed about 20 years ago. But the correlation has drifted considerably in the recent past due to advances in engine infrastructures mainly governed by stringent fuel economy and emission standards.

Gasoline Compression Ignition (GCI) has been identified as a technology which could give both high efficiency and relatively low engine-out emissions. The introduction of any new vehicle technology requires widespread availability of appropriate fuels. It would be ideal therefore if GCI vehicles were able to operate using the standard grade of gasoline that is available at the pump. However, in spite of recent progress, operation at idle and low loads still remains a formidable challenge, given the relatively low autoignition reactivity of conventional gasoline at these conditions. One conceivable solution would be to use both diesel and gasoline, either in separate tanks or blended as a single fuel (“dieseline”). However, with this latter option, a major concern for dieseline would be whether a flammable mixture could exist in the vapour space in the fuel tank.

Fuels are subjected to extreme conditions inside a fuel injector. In modern common rail diesel engines, fuel temperatures can reach 150°C and pressures can exceed 2500 bar inside the rail. Under such conditions the fluid physical properties of the fuel can differ substantially from ambient pressure and temperature and can impact the spray behavior and characteristics. Moreover, experimental determination of the fuel physical properties at these extreme conditions can be very difficult. Previously it has been shown that for pure components, all atom molecular simulations offer a reliable means to calculate the key physical properties (including transport properties, e.g., viscosity) at FIE representative conditions. In this study we extend the approach to calculate these properties of binary mixtures using atomistic molecular simulations.

The effects of lubricant oil and fuel properties on low speed pre-ignition (LSPI) occurrence in boosted S.I. engines were experimentally evaluated with multi-cylinder engine and de-correlated oil and fuel matrices. Further, the auto-ignitability of fuel spray droplets and evaporated homogeneous fuel/oil mixtures were evaluated in a combustion bomb and pressure differential scanning calorimetry (PDSC) tests to analyze the fundamental ignition process. The work investigated the effect of engine conditions, fuel volatility and various lubricant additives on LSPI occurrence. The results support the validity of aspects of the LSPI mechanism hypothesis based on the phenomenon of droplets of lubricant oil/fuel mixture (caused by adhesion of fuel spray on the liner wall) flying into the chamber and autoigniting before spark ignition.

Octane appetite of modern engines has changed as engine designs have evolved to meet performance, emissions, fuel economy and other demands. The octane appetite of seven modern vehicles was studied in accordance with the octane index equation OI=RON-KS, where K is an operating condition specific constant and S is the fuel sensitivity (RONMON). Engines with a displacement of 2.0L and below and different combinations of boosting, fuel injection, and compression ratios were tested using a decorrelated RONMON matrix of eight fuels. Power and acceleration performance were used to determine the K values for corresponding operating points. Previous studies have shown that vehicles manufactured up to 20 years ago mostly exhibited negative K values and the fuels with higher RON and higher sensitivity tended to perform better.

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.