Motored engines

General Motors Engineering Standards. Automotive Engine Coolant, Antifreeze Concentrate-Ethylene Glycol Type, GM 6038-M, Jan. 1971 Automotive Engine Coolant, Concentrate-Ethylene Glycol Type, GM 6043-M, Sept. 1983. 

Baldwin RW, Cunningham GJ, Pratt D. 1964. Carcinogenic action of motor engine oil additives. Br J Cancer 18 503-507. 

Toyota Motor Engineering Manufacturing, North America... 

PREFLAME REACTIONS. During the past 30 years, many workers have associated knock with the preflame reactions occurring prior to rapid combustion. Peroxides and aldehydes are important preflame products. It has become customary to consider these compounds, particularly the former, as important in the knock process (28, 43, 142, 143, 170, 181, 235). Motored engine experiments have tended to confirm this view (42, 46, 154, 136, 157, 174, 103, 225), although Ross (183) has obtained severe knock with n-heptane with no evidence of formation of prereaction products. 

Radiation and Ignition Studies. The existence of cool flame radiation prior to the occurrence of autoignition in a motored engine was discovered early by Peletier, van Hoogstraten, Smittenberg, and Koojman (109). Since then there has been a constant effort to define the engine conditions limiting the occurrence and extent of cool flame radiation with various hydrocarbons (25, 26, 37, 71, 72, 77, 107). 

Motored engine cool flames are discernible with the naked eye only with great difficulty, hence the reliance on detection apparatus for quantitative investigations. The essential features of radiation detection apparatus, such as shown in Figure 1, include a quartz window mounted in the combustion chamber, a photomultiplier radiation detector, and an amplifier-oscilloscope arrangement (107). 

Several hydrocarbons, including benzene, diisobutylene, and methane, do not form cool flames in engines (26, 37, 105). The absence of cool flame radiation does not indicate the absence of preflame reaction, as oxidation products have been isolated from a diisobutylene-air mixture in a motored engine (105). At lean air-fuel ratios, benzene, diisobutylene, and methane have been observed to form blue flames (36). 

The nature of the radiation processes is not fully understood. Ball (10,11), with the aid of a stroboscopic shutter, visually observed cool flames as actual flame fronts moving across the combustion chamber of a motored engine. This was later confirmed by Getz (53). The source of cool flame emission in tube experiments has been attributed to excited formaldehyde by Emeleus (51) and Gaydon (52). Cool flame spectra in engines obtained by Levedahl and Broida (70) and Downs, Street, and Wheeler (35) were reported to be due to excited formaldehyde. The nature of the blue flame spectra has not been fully explored, although some evidence points to carbon monoxide emission (35). 

Recently Livengood, Toong, Rona, Taylor, and Black used an externally heated hot spot to induce surface ignition in a motored engine (53). Under the conditions of these experiments, benzene required a somewhat higher hot-spot temperature for surface ignition than iso-octane, but the difference in temperature was far less than the difference between the spontaneous ignition temperatures of the two hydrocarbons as determined in the laboratory. 

Liquid hydrocarbons are considered to be the most valuable products of a potential recycling process as they can be used as blends for motor engine fuels. In such a process short-chain hydrocarbons in the gas phase are also produced and they are crucial to provide the heat needed for an endothermic reaction such as polymer cracking, bnt their value is considered low due to their transportation cost. 

Examples of the application of motored engines are discussed in Section 6.4 and 6.5. These have contributed significantly not only to the better understanding of the mechanisms of hydrocarbon oxidation but also to a bridging of the gap between the interpretation of reactions investigated in more conventional chemical systems, and the reactions of hydrocarbon fuels in spark-ignition engines. 

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