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Is the “K Value” of an Engine Truly Fuel Independent?

Nissan Motor Co Ltd-Masaharu Kassai, Taisuke Shiraishi
Shell Global Solutions (Deutschland)GmbH-Sandro Gail
  • Technical Paper
  • 2020-01-0615
To be published on 2020-04-14 by SAE International in United States
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, and not dependent on the fuel. 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 and the RON and MON were decorrelated. This simplifies the analysis of the chemical kinetic proprieties. It was shown previously that K increases with engine speed because a higher temperature and pressure is reached along the compression isentrope before knock onset. Through dividing the original fuels 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…
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A Parametric Study of the Flammability of Dieseline Blends with and without Ethanol

Concawe-Heather Hamje, John Rogerson
ENI Spa-Leonardo Pellegrini
Published 2019-01-15 by SAE International in United States
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. Simulations were carried out for dieseline blends containing ethanol with two types of specifications - a fixed ethanol volume percent in the dieseline blend (0-50% ethanol), or blends containing specified EXX gasolines (E10, E20, E30, E40, E60 and E85) added to diesel fuel. Predicted Upper Flammability Limit (UFL) temperatures and blend DVPEs are presented for all…
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Mechanism Analysis on the Effect of Fuel Properties on Knocking Performance at Boosted Conditions

Nissan Motor Co., Ltd.-Masaharu Kassai, Cagdas Aksu, Taisuke Shiraishi
Shell Global Solutions-Roger Cracknell
Published 2019-01-15 by SAE International in United States
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.A new method of interpreting octane appetite is presented which relates the gradient of contour lines of MB50 in RON/MON space to K value.The results can be further interpreted by understanding the relative contribution of low temperature oxidation (LTO) pathways under the prevailing temperature/pressure conditions…
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Investigation of Late Stage Conventional Diesel Combustion - Effect of Additives

Eindhoven University of Technology-P.C. Bakker, Robbert Willems, Nico Dam, Bart Somers
Shell Global Solutions (UK)-Caroline Wakefield, Mark Brewer, Roger Cracknell
Published 2018-09-10 by SAE International in United States
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. To this fuel was added an organic compound, commonly encountered in sunscreen products, that was designed to absorb ultraviolet light.…
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Octane Response of a Highly Boosted Direct Injection Spark Ignition Engine at Different Compression Ratios

Jaguar Land Rover Ltd.-Niall Turner
Shell Global Solutions-Arjun Prakash, Jan-Hendrik Redmann, Roger Cracknell
Published 2018-04-03 by SAE International in United States
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. Prototype engine builds with novel design concepts allow for studying the impact of fuel octane number on engine performance: In this regard, a 2.0 L engine based on…
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A Mathematical Model for the Vapour Composition and Flammability of Gasoline - Diesel Mixtures in a Fuel Tank

Concawe-Heather Hamje, David Rickeard
ENI Spa-Leonardo Pellegrini
Published 2017-10-08 by SAE International in United States
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. The non-ideality of the blends of hydrocarbons and ethanol is accounted for using activity coefficients. Predictions for dry vapour pressure equivalent (DVPE), vapour phase composition and flammability are…
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Octane Requirement and Efficiency in a Fleet of Modern Vehicles

Luebbers Automotive Testing Consultancy-Martin Luebbers
Shell Global Solutions-Roger Cracknell
Published 2017-03-28 by SAE International in United States
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. Therefore as fuel octane number improves, the spark is advanced to the knock boundary of that fuel; a process known as knock limited…
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Injector Fouling and Its Impact on Engine Emissions and Spray Characteristics in Gasoline Direct Injection Engines

SAE International Journal of Fuels and Lubricants

IAV GmbH, Germany-Paul-Benjamin Reinicke, Marc Sens, Michael Rieß
Imperial College London-Sebastian Henkel, Yannis Hardalupas, Alexander Taylor
  • Journal Article
  • 2017-01-0808
Published 2017-03-28 by SAE International in United States
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. Based on these results a selection of the injectors was installed in a laboratory injection chamber and the spray patterns were investigated with a high speed camera. Injectors corresponding to the…
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Open Access

Impact of Fuel Sensitivity (RON-MON) on Engine Efficiency

SAE International Journal of Fuels and Lubricants

Shell Global Solutions-Arjun Prakash, Chongming Wang, Andreas Janssen, Allen Aradi, Roger Cracknell
  • Journal Article
  • 2017-01-0799
Published 2017-03-28 by SAE International in United States
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. In prior research, the octane response of modern engines seemed to correlate better with RON than MON; however, the impact of octane sensitivity (RON-MON) has not been evaluated in detail. In this study, the aforementioned relationship between engine octane appetite and octane sensitivity was studied…
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Determination of Diesel Physical Properties at Injection Pressures and Temperatures via All-Atom Molecular Simulations

SAE International Journal of Fuels and Lubricants

Shell-Abhinav Verma, Roger Cracknell, David Doyle, Indranil Rudra
  • Journal Article
  • 2016-01-2253
Published 2016-10-17 by SAE International in United States
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. We modelled the diesel fuel using two diesel surrogates: a modern “GTL-like” diesel fuel surrogate, n-hexadecane, and a “conventional” diesel fuel surrogate n-decylbenzene and calculated viscosity and density for the respective pure components and their various binary mixtures.The molecular dynamics simulations provide insights into the mechanisms at an atomic level and can reliably calculate…
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