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The Impact of Gasoline Octane on Fuel Economy in Modern Vehicles

Shell Global Solutions U.K.-Christopher Beck, Paul Stevenson, Pauline Ziman
Published 2006-10-16 by SAE International in United States
This paper presents recently derived relationships between gasoline octane quality and vehicle fuel economy measured on a chassis dynamometer. Data are reported from a number of vehicle types, which include both port injection and direct injection technologies. Fuel economy was measured over a fixed test cycle on a matrix of ten fuels. Hence we established an engine/vehicle response to changes in gasoline octane number, in terms of fuel economy. This is comparable with previously reported relationships between gasoline octane quality and engine power output. Finally, fuel economy was measured over a number of industry-standard test cycles, when retail fuels of different octane grade were tested in vehicles. Statistically significant changes in vehicle fuel economy were measured for vehicles that ran on different fuel grades.For over 40 years the octane number of gasoline has been defined by measurements of RON (Research Octane Number) and MON (Motor Octane Number), made in a CFR (Cooperative Fuel Research) engine. Conventional wisdom acknowledges a direct and positive relationship between octane quality and potential engine performance; for example, in modern knock…
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Advantages of Fuels with High Resistance to Auto-ignition in Late-injection, Low-temperature, Compression Ignition Combustion

Shell Global Solutions U.K.-Gautam T. Kalghatgi
Royal Institute of Technology-Per Risberg, Hans-Erik Ångström
Published 2006-10-16 by SAE International in United States
Oxides of nitrogen (NOx) and smoke can be simultaneously reduced in compression ignition engines by getting combustion to occur at low temperatures and by delaying the heat release till after the fuel and air have been sufficiently mixed. One of the ways to obtain such combustion in modern engines using common-rail direct injection is to inject the fuel near top dead centre with high levels of exhaust gas recirculation (EGR) - Nissan MK style combustion. In this work we study the effect of fuel auto-ignition quality, using four fuels ranging from diesel to gasoline, on such combustion at two inlet pressures and different EGR levels. The experiments are done in a 2 litre single-cylinder engine with a compression ratio of 14 at an engine speed of 1200 RPM. The engine can be easily run on gasoline with a single injection near TDC, even though it cannot be run with very early injection, in the HCCI mode. Moreover for any given condition, gasoline has a significantly higher ignition delay for the same combustion phasing and hence…
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Auto-Ignition Quality of Practical Fuels and Implications for Fuel Requirements of Future SI and HCCI Engines

Shell Global Solutions U.K.-Gautam T. Kalghatgi
Published 2005-04-11 by SAE International in United States
The auto-ignition or anti-knock quality of a practical fuel is defined by the Octane Index, OI = (1-K)RON + KMON where RON and MON are the Research and Motor Octane numbers and K is a constant depending only on the pressure and temperature variation in the engine. K decreases as the compression temperature in the unburnt gas at a given pressure in the engine decreases and can be negative if this temperature is lower than in the RON test. As spark ignition (SI) engine designers seek higher efficiency knock becomes more likely. Moreover such initiatives - direct injection, higher compression ratios, downsizing and turbocharging - will reduce the unburnt gas temperature for a given pressure and push the value of K downwards. In Europe there is evidence of a monotonic decrease in the average K value from 1987 to 1992. In 37 different Japanese and European cars (34 models) equipped with knock sensors that have been tested K has been found to be negative in most cases. Thus for a given RON, a fuel of…
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Octane Appetite Studies in Direct Injection Spark Ignition (DISI) Engines

Shell Global Solutions U.K.-Gautam T. Kalghatgi
Toyota Motor Corporation-Koichi Nakata, Kazuhisa Mogi
Published 2005-04-11 by SAE International in United States
The anti-knock or octane quality of a fuel depends on the fuel composition as well as on the engine design and operating conditions. The true octane quality of practical fuels is defined by the Octane Index, OI = (1-K)RON + KMON 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). RON and MON are the Research and Motor Octane numbers respectively, of the fuel. OI is the octane number of the primary reference fuel (PRF) with the same knocking behaviour at the given condition. In this work a wide range of fuels of different RON and MON were tested in prototype direct injection spark ignition (DISI) engines with compression ratios of 11 and 12.5 at different speeds up to 6000 RPM. Knock Limited Spark Advance (KLSA) was used to characterize the anti-knock quality of the fuel. Experiments were also done using two cars with DISI engines equipped with knock sensor systems. The anti-knock quality…
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The Available and Required Autoignition Quality of Gasoline - Like Fuels in HCCI Engines at High Temperatures

Shell Global Solutions U.K.-Gautam T. Kalghatgi, R. A. Head
Published 2004-06-08 by SAE International in United States
In previous work it has been shown that the autoignition quality of a fuel at a given operating condition can be described by its Octane Index, OI = (1-K)RON - KMON; the larger the OI, the more the resistance to autoignition. Here RON and MON are, respectively, the Research and Motor Octane numbers of the fuel and K is a constant depending only on the pressure and temperature history of the fuel / air mixture in the engine prior to autoignition. The value of K is empirically established at a given operating condition by ranking fuels of different RON and MON and of different chemical composition for their ease of autoignition. Another important parameter at a given operating condition is OI0, the Octane Index of the fuel for which heat release is centred at TDC. In previous work K and OI0 were measured at different operating conditions and were related empirically to pressure and temperature of the mixture before autoignition and to engine speed and mixture strength.In this work K and OI0 have been measured…
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Combustion Chamber Deposit Flaking Studies Using a Road Test Procedure

Shell Global Solutions U.K.-Gautam T. Kalghatgi
Published 2002-10-21 by SAE International in United States
A new field problem associated with flakes of combustion chamber deposit (CCD) getting trapped on the exhaust valve seat has been reported by several car manufacturers in Europe. This causes difficulties in start-up and poor driveability. A road test procedure that is reasonably quick and sensitive to fuel changes has been developed to study the deposit flaking problem. The flaking of the deposits is believed to be caused by water - either generated by combustion or existing in the ambient air as water vapour - condensing on the deposits. Water is much more effective than fuel in causing deposit flaking. A way of quantifying the deposit flaking tendency has been defined and its repeatability established based on twenty-nine tests using two different cars and different fuels and additives. There are large differences between base fuels in terms of CCD flaking. Deposit flaking tendency is reduced by running the car in a higher duty cycle or by using conventional detergent additive packages particularly at higher dose rates. The extent of such an effect of additives also…
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