Octane, combustion

The combustion reactions of hydrocarbons—compounds composed of carbon and hydrogen only—are especially important as sources of useful energy. We burn methane, CH4, called natural gas, in our homes to provide heat, and we combust octane, CgHig, in our cars to provide mechanical energy ... 

Motor fuels are submitted to strict regulations concerning physical properties and properties of combustion, for which the octane number is the most representative characteristic. 

The Octane Requirement Increase, ORI, is a phenomenon manifested by the appearance of knocking and is due to the increase in engine octane demand with time. This phenomenon is correlated with the increase of solid deposits in the combustion chamber. Although the causes have not been determined with certainty, some companies have patented additives which modify the deposits. The effect is to limit the increase in octane demand (Bert et al., 1983 Chevron, 1988 Nelson et al., 1989). 

Octane number NF EN 25163 and EN 25164 ISO 5163 and 5164 ASTM D 2700 and 2699 Combustion in a variable compression ratio motor... 

Bert, J.A., J.A. Gething, T.J. Hansel, H.K. Newhall, R.J. Peyla and D.A. Voss (1983), A gasoline additive concentrate removes combustion chamber deposits and reduces vehicle octane requirement . SAE paper No. 83-1709, Fuels and Lubricants meeting, San Francisco, CA. 

Oxygenate Blending octane, 1/2CRON + MON) " Heat of combustion, MJ/ ] Specific gravity Boiling point, °C... 

Octane number is a measure of a fuel s abiUty to avoid knocking. The octane number of a gasoline is deterrnined in a special single-cylinder engine where various combustion conditions can be controlled. The test engine is adjusted to give trace knock from the fuel to be rated. Various mixtures of isooctane (2,2,4-trimethyl pentane) and normal heptane are then used to find the ratio of the two reference fuels that produce the same intensity of knock as that by the unknown fuel. 

Uses. MTBE and related ethers are used to add octane to gasoline. It also adds oxygen to the gasoline, which allows for more efficient combustion, and therefore less carbon monoxide and unbumed hydrocarbon ia the exhaust emissions (11,24). 

The initial process for molecular conversion was thermal reforming (late 1920s). Thermal reforming at 950 - 1050 F and 600 psi produced gasolines of 70 to 80 octane and heavy naphthas less than 40 octane. Products were olefins, diolefins, and aromatic compounds that were unstable in storage and tended to form heavy polymers and gums, which caused combustion problems. 

Higher octane gasoline typically contains a greater proportion of branched alkanes relative to unbranched ones. Are branched alkanes better fuels because they give off more energy on combustion Explain. 

As experiments at Sun Oil Co. in the early 1930s indicated, there were serious disadvantages associated with alcohol. Wliile alcohol did in fact appear to increase the octane number, it left large amounts of deposits in the engine. Alcohol also vaporized out of the gas tank and engine at rapid rates. And the combustion temperature of the alcohol group is lower than for hydrocarbons because it is already partially oxidized. 

Almost all the major car, bus, and truck manufacturers have developed compressed natural gas engines and vehicles. These manufacturers have been able to offer better performance (due to higher octane) and far lower emissions of nitrogen oxides, carbon monoxide, particulate matter, and carbon dioxide to the atmosphere. In 1998, Honda introduced the cleanest internal combustion engine vehicle ever commercially produced the natural gas Civic GX with emissions at one-tenth the state of California s Ultra Low Emission Vehicle standard. Primarily due to the high octane of natural gas, Honda achieved these results without sacrificing performance. 

The deposits formed in internal combustion engines by high-octane petrols may be classed as ashes they consist of mixtures of lead oxides, bromides and sulphates derived from the anti-knock additives and, of course, exert their main corrosive effect on the parts operating at the highest temperature the exhaust valves and the sparking-plug electrodes. 

Combustion of the octane in a poorly tuned engine can produce toxic carbon monoxide along with the usual carbon dioxide and water. In a test of an automobile engine 1.00 L of octane (702 g) is burned, but only 1.84 kg of carbon dioxide is produced. What is the percentage yield of carbon dioxide ... 

Seif-TeS I 6.13A Gasoline, which contains octane, may burn to carbon monoxide if the air supply is restricted. Determine the standard reaction enthalpy for the incomplete combustion of liquid octane in air to carbon monoxide gas and liquid water from the standard reaction enthalpies for the combustions of octane and carbon monoxide ... 

A student rides a bicycle to class every day, a lO.-mile round trip that takes 30. minutes in each direction. The student burns 1250 kj-h 1 cycling. The same round trip in an automobile would require 0.40 gallons of gasoline. Assume that the student goes to class 150 days per year and that the enthalpy of combustion of gasoline can be approximated by that of octane, which has a density of 0.702 g-cm-3 (3.785 F = 1.000 gal). 

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