Ignition and Chemistry of n-Pentane / Ethyl Acetate Fuel Blends

Abstract

Ethyl esters are currently being investigated by the Fuel Science Center at RWTH Aachen University as bio-
derived components for fuel blends. Ethyl esters may be produced from low-grade biomass waste [1] and
may be blended either with traditional hydrocarbon fuels or with other biofuels and sustainably-produced
components.
In order to characterize the kinetic blending behavior of these type of fuels, ethyl acetate was blended with n-
pentane. Mixtures of ethyl acetate and n-pentane were investigated at different blending ratios (1:1, 3:1, 1:3)
in a rapid compression machine at post-compression pressure of 20 bar, equivalence ratio of unity, and over
a temperature range of 630 – 900 K.
In addition, a new chemical kinetic mechanism has been developed, which is based on the mechanisms for
pentane isomers [2] and ethyl esters [3]. Cross-reactions for n-pentane and ethyl acetate were added based
on the reaction classes of Curran et al. [4] with rates estimated either by analogy or with the Reaction
Mechanism Generator [5].
Cross-reactions between n-pentane and ethyl acetate were found to have a measurable effect on the ignition
process, significantly reducing ignition delay time when compared to model predictions excluding cross-
reactions. This is a surprising result as cross-reactions between components in binary fuel blends have been
previously found to have no substantial effect on ignition delay time predictions, e.g. between
dimethoxymethane and n-heptane [6], between ethanol and dimethyl ether [7], and between toluene and
dimethyl ether [8]. The most sensitive cross-reactions for ignition delay times in these experiments are
hydrogen abstraction from n-pentane by peroxy radicals (RO 2 ) of ethyl acetate.

[1] Badawy, T. et al. Fuel 183, 627–640 (2016) doi: 10.1016/j.fuel.2016.06.087
[2] Bugler, J. et al. J. Phys. Chem. A 119, 7510–7527 (2015) doi: 10.1021/acs.jpca.5b00837
[3] Morsch, P. et al., in preparation.
[4] Curran, H. et al. Comb. Flame 114, 149–177 (1998) doi: 10.1016/s0010-2180(97)00282-4
[5] Gao, C. et al. Comp. Phys. Comm. 203, 212–225 (2016) doi: 10.1016/j.cpc.2016.02.013
[6] Jacobs, S. et al. Proc. Comb. Inst. 2020. Under review.
[7] Zhang, Y. et al. Comb. Flame 190, 74–86 (2018) doi: 10.1016/j.combustflame.2017.11.011
[8] Zhang, Y. et al. Proc. Comb. Inst., 36, 413–421 (2017) doi: 10.1016/j.proci.2016.06.190

Full text

Ignition and Chemistry of n-Pentane
/ Ethyl Acetate Fuel Blends
Ethyl esters are currently being investigated by the Fuel
Science Center at RWTH Aachen University as bio-derived
components for fuel blends.
Ethyl esters may be produced from low-grade biomass waste
[1] and may be blended either with traditional hydrocarbon
fuels or with other biofuels and sustainably-produced
components.
Ethyl esters may be employed as the low-reactivity
component in ignition-optimized binary blends
Introduction
M. E. Fuller1, P. Morsch1, and K.A. Heufer1
1Physico-Chemical Fundamentals of Combustion, RWTH Aachen
University, Schinkelstraße 8, 52056 Aachen, Germany
Well-validated pentane base mechanism [2]
Ethyl ester mechanism developed in-group [3]
Cross-reactions for n-pentane and ethyl acetate added based
on the reaction classes of Curran et al. [4]
New rates estimated either by analogy or with the Reaction
Mechanism Generator [5]
Model Development
Results
Measurement of chemical ignition delay time (<2 ms standard
operation, 10 ms with tailored interface)
Typical operating conditions: 10 - 50 bar, 600 - 1400 K
Initial heating up to 150 °C, design pressure 500 bar
Shock Tube (ST)
Single compression stroke with pneumatically-driven,
hydraulically-stopped piston [3]
Variable compression ratio (9 –32)
Rapid Compression Machine (RCM)
Mixtures of ethyl acetate and n-pentane were investigated at
different blending ratios (1:1, 3:1, 1:3) in a rapid compression
machine
Post-compression pressure of 20 bar, equivalence ratio of
unity, and over a temperature range of 630 –900 K.
Cross-reactions between n-pentane and ethyl acetate were
found to have a measurable effect on the ignition process,
significantly reducing ignition delay time when compared to
model predictions excluding cross-reactions.
Observable impacts of cross-reactions on ignition delay time
is a surprising result
Cross-reactions between components in binary fuel blends
have been previously found to have no substantial effect on
ignition delay time predictions, e.g. [6 –8]
The most sensitive cross-reactions for ignition delay times in
these experiments are hydrogen abstraction from n-pentane
by peroxy radicals (RO2) of ethyl acetate.
Effect of cross-reactions: (full
model –solid lines; no cross
–dashed)
Most sensitive cross-
reactions are H abstraction
from pentane by peroxy
radicals (RO2) of ethyl
acetate:
n-C5H12 + REA-O2= C5H11 + REA-
OOH
Conclusions
[1] Badawy, T. et al. Fuel 183 (2016) 627–640
doi: 10.1016/j.fuel.2016.06.087
[2] Bugler, J. et al. J. Phys. Chem. A 119 (2015) 7510–7527
doi: 10.1021/acs.jpca.5b00837
[3] Morsch, P. et al., in preparation.
[4] Curran, H. et al. Comb. Flame 114 (1998) 149–177
doi: 10.1016/s0010-2180(97)00282-4
[5] Gao, C. et al. Comp. Phys. Comm. 203 (2016) 212–225
doi: 10.1016/j.cpc.2016.02.013
[6] Jacobs, S. et al. Proc. Comb. Inst. 2020. Under review.
[7] Zhang, Y. et al. Comb. Flame 190 (2018) 74–86
doi: 10.1016/j.combustflame.2017.11.011
[8] Zhang, Y. et al. Proc. Comb. Inst., 36 (2017) 413–421
doi: 10.1016/j.proci.2016.06.190
References