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72-407: Whether or not a higher octane fuel improves or impairs an engine's performance depends on the design of the engine. In broad terms, fuels with a higher octane rating are used in higher-compression gasoline engines , which may yield higher power for these engines. The added power in such cases comes from the way the engine is designed to compress the air/fuel mixture, and not directly from the rating of

144-406: A bomb calorimeter . Low heat values are calculated from high heat value test data. They may also be calculated as the difference between the heat of formation Δ H f of the products and reactants (though this approach is somewhat artificial since most heats of formation are typically calculated from measured heats of combustion).. For a fuel of composition C c H h O o N n ,

216-415: A knock sensor that monitors if knock is being produced by the fuel being used. In modern computer-controlled engines, the ignition timing will be automatically altered by the engine management system to reduce the knock to an acceptable level. Octanes are a family of hydrocarbons that are typical components of gasoline. They are colorless liquids that boil around 125 °C (260 °F). One member of

288-485: A magneto or an ignition coil . In modern car engines, the ignition timing is managed by an electronic Engine Control Unit . Ignition modules can also function as a rev limiter in some cases to prevent overrevving and the consequences of it, such as valve float and connecting rod failure. Primers may be used to help start the engine. They can draw fuel from fuel tanks and vaporize fuel directly into piston cylinders. Engines are difficult to start during cold weather, and

360-501: A combustion of fuel, measured as a unit of energy per unit mass or volume of substance. In contrast to the HHV, the LHV considers energy losses such as the energy used to vaporize water - although its exact definition is not uniformly agreed upon. One definition is simply to subtract the heat of vaporization of the water from the higher heating value. This treats any H 2 O formed as a vapor that

432-412: A flame wave initiate at the spark plug and then "travel in a fairly uniform manner across the combustion chamber" with the expanding gas mix pushing the piston throughout the entirety of the power stroke. A stable gasoline and air mix will combust when the flame wave reaches the molecules, adding heat at the interface. Knock occurs when a secondary flame wave forms from instability and then travels against

504-439: A lighter fuel that's less prone to autoignition is a wise "insurance policy". For the same reasons, those lighter fuels which are better solvents are much less likely to cause any "varnish" or other fouling on the "backup" spark plugs. In almost all general aviation piston engines, the fuel mixture is directly controlled by the pilot, via a knob and cable or lever similar to (and next to) the throttle control. Leaning — reducing

576-641: A preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 lower than the RON, but there is no direct link between RON and MON. See the table below. In most countries in Europe, and in Australia and New Zealand, the "headline" octane rating prominently displayed on

648-483: A relatively low octane rating; the isomer iso-octane causes less knocking because it is more branched and combusts more smoothly. In general, branched compounds with a higher intermolecular force (e.g., London dispersion force for iso-octane) will have a higher octane rating, because they are harder to ignite. Octane isomers such as n-octane and 2,3,3-trimethylpentane have an octane rating of -20 and 106.1, respectively ( RON measurement). The large differences between

720-412: A steel container at 25 °C (77 °F) is initiated by an ignition device and the reactions allowed to complete. When hydrogen and oxygen react during combustion, water vapor is produced. The vessel and its contents are then cooled to the original 25 °C and the higher heating value is determined as the heat released between identical initial and final temperatures. When the lower heating value (LHV)

792-486: A type of engine used to start a larger, stationary diesel engine. Heat of combustion The heating value (or energy value or calorific value ) of a substance , usually a fuel or food (see food energy ), is the amount of heat released during the combustion of a specified amount of it. The calorific value is the total energy released as heat when a substance undergoes complete combustion with oxygen under standard conditions . The chemical reaction

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864-479: Is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's sensitivity, and is not typically published for those countries that use the Anti-Knock Index labelling system. See the table in the following section for a comparison. Another type of octane rating, called Observed Road Octane Number ( RdON ), is derived from testing

936-480: Is a measured and/or calculated rating of the fuel's ability to resist autoignition, the higher the octane of the fuel, the harder that fuel is to ignite and the more heat is required to ignite it. The result is that a hotter ignition spark is required for ignition. Creating a hotter spark requires more energy from the ignition system, which in turn increases the parasitic electrical load on the engine. The spark also must begin earlier in order to generate sufficient heat at

1008-492: Is a mixture of many hydrocarbons and often other additives). Octane ratings are not indicators of the energy content of fuels. (See Effects below and Heat of combustion ). They are only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced. Ethanol energy density can be compared with gasoline in heat-of-combustion tables. It

1080-446: Is burned in an open flame, e.g. H 2 O (g), Br 2 (g), I 2 (g) and SO 2 (g). In both definitions the products for C, F, Cl and N are CO 2 (g), HF (g), Cl 2 (g) and N 2 (g), respectively. The heating value of a fuel can be calculated with the results of ultimate analysis of fuel. From analysis, percentages of the combustibles in the fuel ( carbon , hydrogen , sulfur ) are known. Since

1152-424: Is determined, cooling is stopped at 150 °C and the reaction heat is only partially recovered. The limit of 150 °C is based on acid gas dew-point. Note: Higher heating value (HHV) is calculated with the product of water being in liquid form while lower heating value (LHV) is calculated with the product of water being in vapor form. The difference between the two heating values depends on the chemical composition of

1224-411: Is possible for a fuel to have a Research Octane Number (RON) more than 100, because iso-octane is not the most knock-resistant substance available today. Racing fuels, avgas , LPG and alcohol fuels such as methanol may have octane ratings of 110 or significantly higher. Typical "octane booster" gasoline additives include MTBE , ETBE , iso-octane and toluene . Lead in the form of tetraethyllead

1296-688: Is recorded in a figurative sense from 1944. By the 1990s, the phrase was commonly being used as a word intensifier, and it has found a place in modern English slang. Petrol engine A petrol engine ( gasoline engine in American and Canadian English) is an internal combustion engine designed to run on petrol ( gasoline ). Petrol engines can often be adapted to also run on fuels such as liquefied petroleum gas and ethanol blends (such as E10 and E85 ). Most petrol engines use spark ignition , unlike diesel engines which typically use compression ignition. Another key difference to diesel engines

1368-430: Is released as a waste. The energy required to vaporize the water is therefore lost. LHV calculations assume that the water component of a combustion process is in vapor state at the end of combustion, as opposed to the higher heating value (HHV) (a.k.a. gross calorific value or gross CV ) which assumes that all of the water in a combustion process is in a liquid state after a combustion process. Another definition of

1440-500: Is that petrol engines typically have a lower compression ratio . The first practical petrol engine was built in 1876 in Germany by Nicolaus August Otto and Eugen Langen , although there had been earlier attempts by Étienne Lenoir in 1860, Siegfried Marcus in 1864 and George Brayton in 1873. Most petrol engines use either the four-stroke Otto cycle or the two-stroke cycle . Petrol engines have also been produced using

1512-434: Is the octane number of the fuel. For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. A rating of 90 does not mean that the gasoline contains just iso-octane and heptane in these proportions, but that it has the same detonation resistance properties (generally, gasoline sold for common use never consists solely of iso-octane and heptane; it

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1584-439: Is the same as the thermodynamic heat of combustion since the enthalpy change for the reaction assumes a common temperature of the compounds before and after combustion, in which case the water produced by combustion is condensed to a liquid. The higher heating value takes into account the latent heat of vaporization of water in the combustion products, and is useful in calculating heating values for fuels where condensation of

1656-440: Is typically a hydrocarbon or other organic molecule reacting with oxygen to form carbon dioxide and water and release heat. It may be expressed with the quantities: There are two kinds of enthalpy of combustion, called high(er) and low(er) heat(ing) value, depending on how much the products are allowed to cool and whether compounds like H 2 O are allowed to condense. The high heat values are conventionally measured with

1728-524: The American Petroleum Institute (API), uses a reference temperature of 60 °F ( 15 + 5 ⁄ 9  °C). Another definition, used by Gas Processors Suppliers Association (GPSA) and originally used by API (data collected for API research project 44), is the enthalpy of all combustion products minus the enthalpy of the fuel at the reference temperature (API research project 44 used 25 °C. GPSA currently uses 60 °F), minus

1800-466: The Miller cycle and Atkinson cycle . Most petrol-powered piston engines are straight engines or V engines . However, flat engines , W engines and other layouts are sometimes used. Wankel engines are classified by the number of rotors used. Petrol engines are either air-cooled or water-cooled . Petrol engines use spark ignition . High voltage for the spark this may be provided by

1872-557: The four-stroke cycle . In a simple explanation, the forward moving wave of combustion that burns the hydrocarbon + oxygen mixture inside the cylinder like a wave that a surfer would wish to surf upon is violently disrupted by a secondary wave that has started elsewhere. The shock wave of these two separate waves creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential (incremental heating plus power loss) to completely destructive (detonation while one of

1944-423: The ideal gas law . Higher compression ratios necessarily add parasitic load to the engine, and are only necessary if the engine is being specifically designed to run on high-octane fuel. Aircraft engines run at relatively low speeds and are " undersquare ". They run best on lower-octane, slower-burning fuels that require less heat and a lower compression ratio for optimum vaporization and uniform fuel-air mixing, with

2016-403: The (higher) heat of combustion is 419 kJ/mol × ( c + 0.3 h − 0.5 o ) usually to a good approximation (±3%), though it gives poor results for some compounds such as (gaseous) formaldehyde and carbon monoxide , and can be significantly off if o + n > c , such as for glycerine dinitrate, C 3 H 6 O 7 N 2 . By convention, the (higher) heat of combustion is defined to be

2088-427: The LHV is the amount of heat released when the products are cooled to 150 °C (302 °F). This means that the latent heat of vaporization of water and other reaction products is not recovered. It is useful in comparing fuels where condensation of the combustion products is impractical, or heat at a temperature below 150 °C (302 °F) cannot be put to use. One definition of lower heating value, adopted by

2160-402: The aircraft of World War II . The octane rating affected not only the performance of the gasoline, but also its versatility; the higher octane fuel allowed a wider range of lean to rich operating conditions. In spark ignition internal combustion engines , knocking (also knock , detonation , spark knock , pinging , or pinking ) occurs when combustion of some of the air/fuel mixture in

2232-402: The available air) or "lean of peak" (less fuel, leaving some oxygen in the exhaust) as either will keep the fuel-air mixture from detonating prematurely. Because of the high cost of unleaded, high-octane avgas , and possible increased range before refueling, some general aviation pilots attempt to save money by tuning their fuel-air mixtures and ignition timing to run "lean of peak". Additionally,

Octane rating - Misplaced Pages Continue

2304-411: The combustion is conducted in a bomb calorimeter containing some quantity of water. Zwolinski and Wilhoit defined, in 1972, "gross" and "net" values for heats of combustion. In the gross definition the products are the most stable compounds, e.g. H 2 O (l), Br 2 (l), I 2 (s) and H 2 SO 4 (l). In the net definition the products are the gases produced when the compound

2376-413: The cylinder does not result from propagation of the flame front ignited by the spark plug , but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for

2448-421: The decreased air density at higher altitudes (such as Colorado) and temperatures (as in summer) requires leaning (reduction in amount of fuel per volume or mass of air) for the peak EGT and power (crucial for takeoff). The selection of octane ratings available at filling stations can vary greatly between countries. Due to its name, the chemical "octane" is often misunderstood as the only substance that determines

2520-480: The definition of octane rating. The following table lists octane ratings for various other fuels. Higher octane ratings correlate to higher activation energies : the amount of applied energy required to initiate combustion. Since higher octane fuels have higher activation energy requirements, it is less likely that a given compression will cause uncontrolled ignition, otherwise known as autoignition, self-ignition, pre-ignition, detonation, or knocking. Because octane

2592-421: The difference is much more significant as it includes the sensible heat of water vapor between 150 °C and 100 °C, the latent heat of condensation at 100 °C, and the sensible heat of the condensed water between 100 °C and 25 °C. In all, the higher heating value of hydrogen is 18.2% above its lower heating value (142   MJ/kg vs. 120   MJ/kg). For hydrocarbons, the difference depends on the hydrogen content of

2664-597: The direct measurements required for research or motor octane numbers. An octane index can be of great service in the blending of gasoline. Motor gasoline, as marketed, is usually a blend of several types of refinery grades that are derived from different processes such as straight-run gasoline, reformate, cracked gasoline etc. These different grades are blended in amounts that will meet final product specifications. Most refiners produce and market more than one grade of motor gasoline, differing principally in their anti-knock quality. Being able to make sufficiently accurate estimates of

2736-405: The end of the compression stroke by electric spark plugs . Therefore, being able to compress the air/fuel mixture without causing detonation is important mainly for gasoline engines. Using gasoline with lower octane than an engine is built for may cause engine knocking and/or pre-ignition . The octane rating of aviation gasoline was extremely important in determining aero engine performance in

2808-507: The engine. Lighter and "thinner" fuel also has a lower specific heat , so the practice of running an engine "rich" to use excess fuel to aid in cooling requires richer and richer mixtures as octane increases. Higher-octane, lower-energy-dense "thinner" fuels often contain alcohol compounds incompatible with the stock fuel system components, which also makes them hygroscopic . They also evaporate away much more easily than heavier, lower-octane fuel which leads to more accumulated contaminants in

2880-445: The enthalpy of the stoichiometric oxygen (O 2 ) at the reference temperature, minus the heat of vaporization of the vapor content of the combustion products. The definition in which the combustion products are all returned to the reference temperature is more easily calculated from the higher heating value than when using other definitions and will in fact give a slightly different answer. Gross heating value accounts for water in

2952-401: The evaluation of the anti-knock quality of gasoline. Such substitute methods include FTIR, near infrared on-line analyzers, and others. Deriving an equation that can be used to calculate ratings accurately enough would also serve the same purpose, with added advantages. The term Octane Index is often used to refer to the use of an equation to determine a theoretical rating, in contradistinction to

Octane rating - Misplaced Pages Continue

3024-449: The exhaust leaving as vapor, as does LHV, but gross heating value also includes liquid water in the fuel prior to combustion. This value is important for fuels like wood or coal , which will usually contain some amount of water prior to burning. The higher heating value is experimentally determined in a bomb calorimeter . The combustion of a stoichiometric mixture of fuel and oxidizer (e.g. two moles of hydrogen and one mole of oxygen) in

3096-642: The fuel primer helps because otherwise there will not be enough heat available to vaporize the fuel in the carburetor . The power output of small- and medium-sized petrol engines (along with equivalent engines using other fuels) is usually measured in kilowatts or horsepower . Typically, petrol engines have a thermodynamic efficiency of about 20-30% (approximately half that of some diesel engines). Applications of petrol engines include automobiles , motorcycles , aircraft , motorboats and small engines (such as lawn mowers, chainsaws and portable generators). Petrol engines have also been used as "pony engines",

3168-405: The fuel system. It is typically the hydrochloric acids that form due to that water and the compounds in the fuel that have the most detrimental effects on the engine fuel system components, as such acids corrode many metals used in gasoline fuel systems. During the compression stroke of an internal combustion engine, the temperature of the air-fuel mix rises as it is compressed, in accordance with

3240-460: The fuel. For gasoline and diesel the higher heating value exceeds the lower heating value by about 10% and 7%, respectively, and for natural gas about 11%. A common method of relating HHV to LHV is: where H v is the heat of vaporization of water, n H 2 O ,out is the number of moles of water vaporized and n fuel,in is the number of moles of fuel combusted. Engine manufacturers typically rate their engines fuel consumption by

3312-408: The fuel. In the case of pure carbon or carbon monoxide, the two heating values are almost identical, the difference being the sensible heat content of carbon dioxide between 150 °C and 25 °C ( sensible heat exchange causes a change of temperature, while latent heat is added or subtracted for phase transitions at constant temperature. Examples: heat of vaporization or heat of fusion ). For hydrogen,

3384-400: The gasoline in ordinary multi-cylinder engines (rather than in a purpose-built test engine), normally at wide open throttle. This type of test was developed in the 1920s and is still reliable today. The original RdON tests were done in cars on the road, but as technology developed the testing was moved to chassis dynamometers with environmental controls to improve consistency. The evaluation of

3456-400: The gasoline. In contrast, fuels with lower octane (but higher cetane numbers ) are ideal for diesel engines because diesel engines (also called compression-ignition engines) do not compress the fuel, but rather compress only air, and then inject fuel into the air that was heated by compression. Gasoline engines rely on ignition of compressed air and fuel mixture, which is ignited only near

3528-496: The heat of combustion of these elements is known, the heating value can be calculated using Dulong's Formula: HHV [kJ/g]= 33.87m C + 122.3(m H - m O ÷ 8) + 9.4m S where m C , m H , m O , m N , and m S are the contents of carbon, hydrogen, oxygen, nitrogen, and sulfur on any (wet, dry or ash free) basis, respectively. The higher heating value (HHV; gross energy , upper heating value , gross calorific value GCV , or higher calorific value ; HCV ) indicates

3600-613: The heat released for the complete combustion of a compound in its standard state to form stable products in their standard states: hydrogen is converted to water (in its liquid state), carbon is converted to carbon dioxide gas, and nitrogen is converted to nitrogen gas. That is, the heat of combustion, Δ H ° comb , is the heat of reaction of the following process: Chlorine and sulfur are not quite standardized; they are usually assumed to convert to hydrogen chloride gas and SO 2 or SO 3 gas, respectively, or to dilute aqueous hydrochloric and sulfuric acids , respectively, when

3672-476: The higher heating value will be somewhat higher. The difference between HHV and LHV definitions causes endless confusion when quoters do not bother to state the convention being used. since there is typically a 10% difference between the two methods for a power plant burning natural gas. For simply benchmarking part of a reaction the LHV may be appropriate, but HHV should be used for overall energy efficiency calculations if only to avoid confusion, and in any case,

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3744-449: The ignition spark coming as late as possible in order to extend the production of cylinder pressure and torque as far down the power stroke as possible. The main reason for using high-octane fuel in air-cooled engines is that it is more easily vaporized in a cold carburetor and engine and absorbs less intake air heat which greatly reduces the tendency for carburetor icing to occur. With their reduced densities and weight per volume of fuel,

3816-443: The lifespan of engines. In 1927, Graham Edgar devised the method of using iso-octane and n-heptane as reference chemicals, in order to rate the knock resistance of a fuel with respect to this isomer of octane, thus the name "octane rating". By definition, the isomers iso-octane and n-heptane have an octane rating of 100 and 0, respectively. Because of its more volatile nature, n-heptane ignites and knocks readily, which gives it

3888-442: The lower heating values since the exhaust is never condensed in the engine, and doing this allows them to publish more attractive numbers than are used in conventional power plant terms. The conventional power industry had used HHV (high heat value) exclusively for decades, even though virtually all of these plants did not condense exhaust either. American consumers should be aware that the corresponding fuel-consumption figure based on

3960-653: The lower of the two. One is referred to as the "aviation lean" rating, which for ratings up to 100 is the same as the MON of the fuel. The second is the "aviation rich" rating and corresponds to the octane rating of a test engine under forced induction operation common in high-performance and military piston aircraft. This utilizes a supercharger , and uses a significantly richer fuel/air ratio for improved detonation resistance. The most common currently used fuel, 100LL , has an aviation lean rating of 100 octane, and an aviation rich rating of 130. The RON/MON values of n- heptane and iso-octane are exactly 0 and 100, respectively, by

4032-444: The mixture from its maximum amount — must be done with knowledge, as some combinations of fuel mixture and throttle position (that produce the highest ) can cause detonation and/or pre-ignition , in the worst case destroying the engine within seconds. Pilots are taught in primary training to avoid settings that produce the highest exhaust gas temperatures, and run the engine either "rich of peak EGT " (more fuel than can be burned with

4104-479: The octane family, 2,2,4-Trimethylpentane (iso-octane), is used as a reference standard to benchmark the tendency of gasoline or LPG fuels to resist self-ignition. The octane rating of gasoline is measured in a test engine and is defined by comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and normal heptane that would have the same anti-knocking capability as the fuel under test. The percentage, by volume, of 2,2,4-trimethylpentane in that mixture

4176-401: The octane number by either of the two laboratory methods requires a special engine built to match the tests' rigid standards, and the procedure can be both expensive and time-consuming. The standard engine required for the test may not always be available, especially in out-of-the-way places or in small or mobile laboratories. These and other considerations led to the search for a rapid method for

4248-492: The octane rating (or octane number) of a fuel. This is an inaccurate description. In reality, the octane rating is defined as a number describing the stability and ability of a fuel to prevent an engine from unwanted combustions that occur spontaneously in the other regions within a cylinder (i.e., delocalized explosions from the spark plug). This phenomenon of combustion is more commonly known as engine knocking or self-ignition, which causes damage to pistons over time and reduces

4320-414: The octane rating of gasoline is not directly related to the power output of an engine. Using gasoline of a higher octane than an engine is designed for cannot increase its power output. Octane became well known in American popular culture in the 1960s, when gasoline companies boasted of "high octane" levels in their gasoline advertisements. The compound adjective "high-octane", meaning powerful or dynamic,

4392-403: The octane rating that will result from blending different refinery products is essential, something for which the calculated octane index is specially suited. Aviation gasolines used in piston aircraft engines common in general aviation have a slightly different method of measuring the octane of the fuel. Similar to an AKI, it has two different ratings, although it is usually referred to only by

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4464-417: The octane ratings for the isomers show that the compound octane itself is clearly not the only factor that determines octane ratings, especially for commercial fuels consist of a wide variety of compounds. "Octane" is colloquially used in the expression "high-octane". The term is used to describe a powerful action because of the association with the concept of "octane rating". This is a misleading term, because

4536-543: The other obvious benefit is that an aircraft with any given volume of fuel in the tanks is automatically lighter. And since many airplanes are flown only occasionally and may sit unused for weeks or months, the lighter fuels tend to evaporate away and leave behind fewer deposits such as "varnish" (gasoline components, particularly alkenes and oxygenates slowly polymerize into solids). Aircraft also typically have dual "redundant" ignition systems which are nearly impossible to tune and time to produce identical ignition timing, so using

4608-452: The path of the primary flame wave, thus depriving the power stroke of its uniformity and causing issues including power loss and heat buildup. The other rarely-discussed reality with high-octane fuels associated with "high performance" is that as octane increases, the specific gravity and energy content of the fuel per unit of weight are reduced. The net result is that to make a given amount of power , more high-octane fuel must be burned in

4680-415: The proper time for precise ignition. As octane, ignition spark energy, and the need for precise timing increase, the engine becomes more difficult to "tune" and keep "in tune". The resulting sub-optimal spark energy and timing can cause major engine problems, from a simple "miss" to uncontrolled detonation and catastrophic engine failure. Mechanically within the cylinder, stability can be visualized as having

4752-637: The pump is the RON, but in Canada, the United States, and Mexico, the headline number is the simple mean or average of the RON and the MON, called the Anti-Knock Index ( AKI ), and often written on pumps as (R+M)/2 . AKI is also sometimes called PON (Pump Octane Number). Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States

4824-457: The reaction products is practical (e.g., in a gas-fired boiler used for space heat). In other words, HHV assumes all the water component is in liquid state at the end of combustion (in product of combustion) and that heat delivered at temperatures below 150 °C (302 °F) can be put to use. The lower heating value (LHV; net calorific value ; NCV , or lower calorific value ; LCV ) is another measure of available thermal energy produced by

4896-457: The results with those for mixtures of iso-octane and n-heptane. The compression ratio is varied during the test to challenge the fuel's antiknocking tendency, as an increase in the compression ratio will increase the chances of knocking. Another type of octane rating, called Motor Octane Number ( MON ), is determined at 900 rpm engine speed instead of the 600 rpm for RON. MON testing uses a similar test engine to that used in RON testing, but with

4968-415: The upper limit of the available thermal energy produced by a complete combustion of fuel. It is measured as a unit of energy per unit mass or volume of substance. The HHV is determined by bringing all the products of combustion back to the original pre-combustion temperature, including condensing any vapor produced. Such measurements often use a standard temperature of 25 °C (77 °F; 298 K) . This

5040-417: The value or convention should be clearly stated. Both HHV and LHV can be expressed in terms of AR (all moisture counted), MF and MAF (only water from combustion of hydrogen). AR, MF, and MAF are commonly used for indicating the heating values of coal: The International Energy Agency reports the following typical higher heating values per Standard cubic metre of gas: The lower heating value of natural gas

5112-458: The valves is still open). Knocking should not be confused with pre-ignition —they are two separate events with pre-ignition occurring before the combustion event. However, pre-ignition is highly correlated with knock because knock will cause rapid heat increase within the cylinder eventually leading to destructive pre-detonation. Most engine management systems commonly found in automobiles today, typically electronic fuel injection (EFI), have

5184-485: Was once a common additive, but concerns about its toxicity have led to its use for fuels for road vehicles being progressively phased out worldwide beginning in the 1970s. The most common type of octane rating worldwide is the Research Octane Number ( RON ). RON is determined by running the fuel in a test engine at 600 rpm with a variable compression ratio under controlled conditions, and comparing

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