AUTOIGNITION OF N-HEPTANE, ETHANOL, METHYL HEXANOATE AND METHYL 3-HEXENOATE IN A MOTORED ENGINE

Open Access
Author:
Moyer, Orin D
Graduate Program:
Energy and Mineral Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Dr Boehman, Thesis Advisor
  • Andre Louis Boehman, Thesis Advisor
Keywords:
  • methyl hexenoate
  • C7
  • motored engine
  • esters
  • biodiesel
  • CFR
  • methyl hexanaote
  • autoignition
Abstract:
Autoignition of fuel blends consisting of ethanol, n-heptane, and two biodiesel surrogates: methyl hexanoate (mhx) and methyl 3-hexenoate (m3h) were studied in a Cooperative Fuels Research (CFR) motored-engine at equivalence ratios (¥Õ) 0.25 and 0.50 (typical ¥Õ of HCCI and diesel engine operation) with an intake temperature of 155¨¬C. The objectives of the study were to further understand the low-temperature oxidation chemistry of the four pure fuels and their blends, to compare the effect of a saturated and unsaturated methyl ester containing the same number of carbon atoms as n-heptane, to observe the intermediate species by GS-MS and GC-FID examination of exhaust samples taken prior to the autoignition event, and to study the impact of ethanol on each of the methyl esters . The compression ratio of the CFR engine was gradually increased from the lowest point to the point where the onset of high-temperature heat-release (HTHR) occurred. Within the test range of this research, all fuels and their blends where driven to their critical compression ratio (the onset of HTHR); and it was observed through heat-release analysis and of CO emissions trends comparison that the saturated methyl ester (mhx) exhibited cool-flame behavior while its unsaturated counterpart did not. This observation agrees with previous studies by Zhang and Boehman that the presence of a double-bond in the aliphatic chain suppresses cool-flame behavior by inhibiting isomerization reactions of peroxy radicals that are key to low-temperature oxidation chemistry. All blends with ethanol had a roughly linear effect on the delay of the onset of HTHR. Another trend observed was that blends with increasing ethanol content had a lower magnitude of LTHR and an onset occurring further after top dead center at the same compression ratio indicating that blends with increasing ethanol content are less reactive in the low-temperature regime. Interestingly, the magnitude of LTHR increases with increasing compression ratio for mhx/hept blends while the magnitude of LTHR was noted to decrease for pure mhx. Further, it was observed that the magnitude of the LTHR at the critical compression ratio decreases with increasing ethanol content for pure mhx and its n-heptane blends as a result of the inhibiting effect of ethanol on ignition.