Gasoline Combustion - Effect of Boron or Silicon Compounds

Abstract

Continued operation of internal combustion engines results in the formation of a thin deposit of carbonaceous material and inorganic lead compounds over most of the exposed surfaces of the combustion chamber. These deposits increase to an equilibrium thickness and cause the octane requirement of the engine to increase 10 to 15 units. Full scale engine studies showed that small amounts of borates, borines, ethyl sulfate, and silicone added to leaded fuels largely repressed this octane requirement increase. These observations are correlated with laboratory studies which showed a difference in the catalytic effect between the oxides of boron and silicon and lead sulfate, and the components of the combustion zone deposits on the oxidation of ra-heptane.The boron compounds and silicone do not provide a complete answer to the problem of engine deposit harm, as they were found to be ineffective in engines already containing deposits. However, the ability of these compounds to affect the nature of these deposits offers encouragement in solving the problem in the future and lends support to a catalytic rather than thermal conductivity theory as an explanation of the cause of octane requirement increase.

Effect of Boron Compounds on Combustion Processes

“…These consisted of a laboratory medium-duty cycle test under the conditions shown in Table VI, a high speed turnpike test in passenger cars (Table VII), and a valve-life test in trucks overloaded and run at high speed. Earlier results (13) had shown much less octane requirement increase with a fuel containing a boron compound. However, these tests did not-show any important reduction in equilibrium octane requirement.…”

“…J3oRON compounds have been reported by several authors to have a variety of interesting effects on the oxidation of hydrocarbons, gasoline, and carbon (19,20,22). In engines a reduction in the octane requirement increase has been observed (6,9,13,15).…”

“…Sabina and coworkers (21) point out also that the prevention in the preflame period of the conversion of carbon monoxide to carbon dioxide is important and that this is normally a catalytic step. We have noted that boric oxide coated on porcelain or steel would eliminate their catalytic influence on the conversion of carbon monoxide to carbon dioxide in the oxidation of heptane (12,13). Nebel and Cramer (16) of General Motors showed that whereas their sample of carbon would glow in air at 1030°F ., the common lead basic halides which occur in leaded gasoline deposits would reduce the glow point to 605°to 650°F.…”

Preparation, Properties, and Uses of Borate Esters

“…In general, for esters which hydrolyze rapidly, it seems reasonable to ascribe the prin cipal effects to the resulting alcohol or (phenol) and boric acid. Boric acid is said to (132,177,178) (162) (10, 19,31, 60, 68-71, 148, 160) (6,126,168,195) (44,54,49,117,154) (44, 54,174,190) (64) (99) (52,67,88,117) (122) (10, 11, 19, 31, 4^, 43, 50, 51, 125, 152, 189 (18, 31, 80, 103, 138, 162, 178) (10,19,31,138,150) (46,138) (10,19,31) (10, 13, 19, 22, 28, 31, 82, 46, 57, 82, 89, In METAL-ORGANIC COMPOUNDS; Advances in Chemistry; American Chemical Society: Washington, DC, 1959. affect the central nervous system and to accumulate in the brain, liver, and body fat. Sax states that the fatal dose of orally ingested boric acid is 15 to 20 grams for adults and 5 to 6 grams for infants.…”

Mechanism of Combustion Chamber Deposit Formation with Leaded Fuels

“…formation of deposits on the combustion chamber walls during normal operation of Otto-cycle engines increases the tendency of fuels to knock. Some of the factors responsible for this effect have been described (3,4,6), but very little information is available about the reaction mechanisms which result in the accumulation of these deposits from fuels containing tetraethyllead. Because such information would give a better understanding of ways to prevent or reduce deposit formation, a study of these reactions was undertaken at the Du Pont laboratories.…”