The Initiation of the Pre-Flame Reaction of n-Heptane in a Motored Engine

Abstract

A motored, unfired CFR engine was red with a rich heptane/air mixture. The jacket temperature was maintained at lOOcC with a few experiments at Oee. The ·exhaust vapours were totally condensed by a novel exhaust recovery system. After completely removing cylinder deposits. no reaction products were round at compression ratios up to 14: I. At a compression ratio or 16: I the charge autoignited/detonated. Subsequently, reaction products were round at a compression ratio or 6: I and thereafter in increasing quantities up to 14.6: I, the reproducible threshold of autoignition. This entire sequence or experiments was reproduced four times. Samples of the condensate were concentrated by vacuum distillation and subjected to qualitative and quantitative analyses. A very limited range of peroxides and carbonyls were formed in very low concentrations in all experiments where autoignition did not occur. These were identified and their rates of formation calculated. Some thermodynamic inferences were drawn as to their heats of formation. The maximum compression temperatures were calculated. At compression ratios below 16: I, it was concluded that the preflame reaction was initiated on the surface or the combustion chamber, after it had been subjected to autoignitions/detonations,

Gasoline Surrogate Oxidation in a Motored Engine, a JSR, and an RCM: Characterization of Cool-Flame Products by High-Resolution Mass Spectrometry

“…Several studies have highlighted the formation of peroxidic compounds during n -heptane oxidation in flow systems, motored engines, − and JSRs . Hydroperoxides can be formed during alkane’s low-temperature oxidation via well-established combustion chemistry reactions: fuel (RH) + X • ( • OH, HO 2 • , H • , O • , ...) → R • + XH; R • + O 2 → ROO • ; ROO • + HO 2 • → ROOH + O 2 .…”

“…Species with three carbonyl groups, known as triketones (C 7 H 10 O 3 and C 8 H 12 O 3 ), can be formed from the decomposition of diketo-hydroperoxide intermediates (C 7 H 12 O 4 and C 8 H 14 O 4 ): (HOO)­P­(O) 2 + X • → (HOO)­P • (O) 2 + HX → P­(O) 3 + • OH. Triketones, such as 2,4,6-heptanetrione, have been identified during n -heptane oxidation under motored engine conditions . Signals corresponding to C 7 H 10 O 3 and C 8 H 12 O 3 were detected by UHPLC coupled to APCI­(+/−)/HRMS (C 7 H 11 O 3 + with m / z 143.0700, C 7 H 9 O 3 – with m / z 141.0556, C 8 H 13 O 3 + with m / z 157.0857, and C 8 H 11 O 3 – with m / z 155.0713), as shown in Supporting Information, Figure S4.…”

“…Experimental conditions for the oxidation of a PRF 50 mixture in JSR and RCM, are summarized in Table 2. Several studies have highlighted the formation of peroxidic compounds during n-heptane oxidation in flow systems 23 , motored engines [24][25][26][27] , and JSRs ). Hence, one can deduce that the olefinic hydroperoxides from n-heptane are likely more abundant than those from iso-octane.…”