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The transport of fuel-borne additives into the engine oil is a critical factor for the efficacy with which the additive functionality can be imparted on the engine. This paper describes the combination of Laser Induced Fluorescence (LIF) and Liquid Chromatography (LC) to determine the real-time additive concentrations and transfer ratios in a spark-ignition, 2-liter GM LHU engine. The current research used a continuous sample circuit from the engine sump which passed through an integrating cavity flow cell to enhance the LIF signal. In the absence of a fluorescence signature of any of the native additive species, a suitable fluorescing dye was selected to simulate the additive. After establishing rigorous calibration curves, LC was employed as a referee method to do a direct comparison with the LIF determined dye concentrations.

Low-Speed Pre-ignition (LSPI) is an undesirable abnormal combustion phenomenon observed in turbocharged, direct-injection spark-ignition engines and is characterized by early heat release, high cylinder pressures and severe, potentially damaging knock. LSPI has been studied for more than a decade and engine design, operating conditions and fuel and engine oil formulations have all been identified as contributing factors. A significant focus on engine oil has led to the establishment of the Sequence IX engine test and the second-generation of GM dexos® oil requirements, as well as a convergence of engine oil detergent causality. Conclusions about the effects of fuel on LSPI have been more varied, but as part of a recently completed research consortium, the LSPI tendency of market fuels with a range of properties, including composition, boiling point distribution, ethanol content and particulate matter index (PMI) were evaluated.

The confluence of increasing fuel economy requirements and increased use of ethanol as a gasoline blend component has led to various studies into the efficiency and performance benefits of higher octane numbers and high ethanol content fuels in modern engines. As part of a comprehensive study of the autoignition of different fuels in both the CFR octane rating engine and a modern, direct injection, turbocharged spark-ignited engine, a series of fuel blends were prepared with varying composition, octane numbers and ethanol blend levels. The paper reports on the third part of this study where cylinder pressures were recorded for fuels under knocking conditions in both a single-cylinder research engine (SCE), utilizing a GM LHU head and piston, as well as the CFR engines used for octane ratings.

It is widely acknowledged that the CFR octane rating engines are not representative of modern engines and that there is a gap in the quantification of knock severity between the two engine types. As part of a comprehensive study of the autoignition of different fuels in both the CFR octane rating engines and a modern, direct injection, turbocharged spark-ignited engine, a series of fuel blends were tested with varying composition, octane numbers and ethanol blend levels. The paper reports on the fourth part of this study where cylinder pressures were recorded under standard knock conditions in CFR engines under RON and MON conditions using the ASTM prescribed instrumentation. By the appropriate signal conditioning of the D1 detonation pickups on the CFR engines, a quantification of the knock severity was possible that had the same frequency response as a cylinder pressure transducer.

Stochastic or Low-Speed Preignition (SPI or LSPI) is an undesirable abnormal combustion phenomenon encountered in spark-ignition engines. It is characterized by very early heat release and high cylinder pressure and can cause knock, noise and ultimately engine damage. Much of the focus on mitigating SPI has been directed towards the engine oil formulation, leading to the emergence of the Sequence IX test and second-generation GM dexos® oil requirements. Engine design, calibration and fuels also contribute to the prevalence of SPI. As part of a recently completed research consortium, a series of engine tests were completed to determine the impact of fuel composition on SPI frequency. The fuel blends had varying levels of paraffins, olefins, aromatics and ethanol.

The confluence of fuel economy improvement requirements and increased use of ethanol as a gasoline blend component has led to various studies into the efficiency and performance benefits to be had when using high octane number, high ethanol content fuels in modern engines. As part of a comprehensive study of the autoignition of fuels in both the CFR octane rating engine and a modern, direct injection, turbocharged spark ignited engine, a series of fuel blends were prepared with market relevant ranges of octane numbers and ethanol blends levels. The paper reports on the first part of this study where fuel flow measurements were done on a single cylinder research engine, utilizing a GM LHU combustion system, and then used to predict drive cycle fuel economy. For a range of engine speeds and manifold air pressures, spark timing was adjusted to achieve either the maximum brake torque (MBT) or a matched 50 % mass fraction burnt location.

Dual injection fuel systems combine the knock and fuel economy benefits of gasoline direct injection (GDI) technology with the lower particulate emissions of port fuel injection (PFI) systems. For many years, this technology was limited to smaller-volume, high-end, vehicle models, but these technologies are now becoming main stream. The combination of two fuel injection systems has an impact on the combustion emission composition as well as the consistency of control strategy and emissions. Understanding the impact of these changes is essential for fuel and fuel additive companies, automotive companies, and aftertreatment developers. This paper describes the effects of dual injection technology on both regulated and non-regulated combustion emissions from a 2018 Toyota Camry during several cold-start, 4-bag United States Federal Test Procedure (FTP) cycle.

This paper reports on the comprehensive applications testing of the first commercial volumes of Gas-to-Liquids (GTL) diesel produced via the Sasol Slurry Phase Distillate™ (Sasol SPD™) process, a Low Temperature Fischer-Tropsch (LTFT) process, at the Oryx GTL plant in Qatar. The technical literature is well populated with results of emissions and applications studies of GTL diesel; however, these results have been limited to product produced at pilot plant and relatively small commercial scale. To ensure that diesel produced commercially not only matches the performance of material previously produced at pilot plant scale using the same technology, but is also fit-for-purpose in the broader sense, a series of chemical assessments and applications testing was performed using both neat and blended diesel fuels. These included emissions tests in passenger cars and heavy-duty applications, engine durability, injector fouling performance and a passenger car fleet trial.

The ASTM D6890 method predicts cetane numbers of diesel fuels based on the measured ignition delay in a combustion bomb (Ignition Quality Tester™). The device is calibrated using n-heptane as the reference fuel. When n-heptane was tested in the IQT™ device over a range of temperatures and pressures, the measured ignition delay did not correlate with the chemical autoignition delay normally associated with a stoichiometric, homogeneous mixture as predicted by detailed chemical kinetic models. This paper describes an investigation to study and reconcile this discrepancy, using (CFD) techniques to explore the physical conditions prevailing in the IQT™ device. Significant insights regarding the flow patterns, thermal gradients and air/fuel ratio profiles were obtained from the analysis. The calculation yielded ignition-delay predictions (defined by the first appearance of a local autoignition) that correlated well with IQT™ experimental data.

The paper describes the emulation of the knock measurement equipment on the CFR engine used during octane rating. It was found during engine measurements that the low-pass filtered rate-of-change of the pressure signal from Primary Reference Fuels (PRF) established the definitive metric of standard knock intensity and that non-PRF fuels exhibited similar pressure rise rates at standard knock intensity. The effect of fuel octane number, compression ratio and air-fuel ratio was also clearly distinguishable. Further modelling interpretation revealed that a non-instantaneous, cascading autoignition was a likely origin for the measured pressure development. Thermal inhomogeneities, which were the result of a heat loss gradient in the trapped mass, served to explain the observed behaviour of both RON and MON test conditions and a range of fuels of different octane numbers.

Careful consideration of the development and operation of the ASTM knock detection system on the Cooperative Fuels Research (CFR) octane rating engine has shown that the pressure fluctuations, brought about by autoignition of the end-gas, do not contribute to measurement of knock intensity. The analyses of a variety of fuels at standard knock intensity revealed that knock intensity measured on the CFR engine is related to the rate of change of pressure prior to knocking and is consistent with the description and operation of, not only the original bouncing pin, but also the modern day electronic CFR knock measurement system. It was concluded that the use of octane number data to directly infer information about the autoignition behaviour of fuels should be done with caution.

The paper studied the burn rate of fuels in the CFR engine at standard knock intensity. Burn duration was found to increase with compression ratio, and knocking pressure traces exhibited a distinct change in slope, thought to be the onset of knock. A criterion was developed to identify this knock-point. The knock-point was related to the mass fraction bunt and it was found that the mass fraction burnt at the knock-point decreases as the compression ratio decreases, to as little as 30%. It is proposed that the nature of knock in the CFR engine is unique in that a large fraction of the trapped mass participates in the autoignition. The paper also presented a functional descriptor for the mass fraction burnt and illustrated the suitability thereof through the application in an engine model.

A recently approved method for cetane determination using the Ignition -Quality Tester (IQT™) is based on an ignition delay measurement in a combustion bomb apparatus, which is empirically correlated to cetane number. The correlation assumes that all fuels will respond to the different pressure and temperature domains of the IQT™ and the cetane test engine in the same way. This assumption was investigated at a more fundamental level by conducting IQT™ measurements at different pressure and temperature points and characterising the ignition delay of the fuel in terms of an Arrhenius autoignition model. The fuel model was combined with a mathematical model of the cetane engine and the concept was evaluated using a variety of test fuels, including the diesel cetane rating reference fuels. The analysis technique was able to accurately predict the cetane number in all cases.