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Research Papers: Gas Turbines: Industrial & Cogeneration

# Effects of a Low Octane Gasoline Blended Fuel on Negative Valve Overlap Enabled HCCI Load Limit, Combustion Phasing and Burn Duration

[+] Author and Article Information
Luke M. Hagen

e-mail: lumoha@umich.edu

Laura Manofsky Olesky

e-mail: manofsky@umich.edu

Stanislav V. Bohac

e-mail: sbohac@umich.edu

George Lavoie

e-mail: glavoie@umich.edu
Department of Mechanical Engineering,
University of Michigan,
Ann Arbor, MI 48109

Dennis Assanis

Office of the Provost,
Stony Brook University,
Stony Brook, NY 11794
e-mail: dennis.assanis@stonybrook.edu

1Dennis Assanis is the former Jon R. and Beverly S. Holt Professor of Engineering, and former Director of the Walter E. Lay Automotive Laboratory at the University of Michigan. He is presently the Provost and Senior Vice President for Academic Affairs at Stony Brook University, and VP for Brookhaven Affairs.

Contributed by the IC Engineering Division of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received November 18, 2012; final manuscript received November 26, 2012; published online June 12, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(7), 072001 (Jun 12, 2013) (10 pages) Paper No: GTP-12-1439; doi: 10.1115/1.4023885 History: Received November 18, 2012; Revised November 26, 2012

## Abstract

Homogeneous charge compression iginition (HCCI) combustion allows for the use of fuels with octane requirements below that of spark-ignited engines. A reference gasoline was compared with iso-octane and a low octane blend of gasoline and 40% n-heptane, NH40. Experiments were conducted on a single cylinder engine operating with negative valve overlap (NVO). The fuel flow rate per cycle was compensated based on the lower heating value to maintain a constant energy addition across fuels. Iso-octane and gasoline demonstrated similar maximum load, achieving a gross $IMEPg$ of $~430$ kPa, whereas the NH40 demonstrated an increased $IMEPg$ of $~$460 kPa. The NH40 could be operated at a later phasing compared with the higher octane fuels, and exhibited a shorter burn duration at a given fueling rate and phasing. These results could be due to compositional differences, as NH40 required less NVO compared to iso-octane and gasoline, leading to less thermal and compositional stratification, as well as a higher $O2$ concentration and less residual gas. Additionally, the NH40 fuel demonstrated a higher intermediate temperature heat release than the higher octane fuels, potentially contributing to the shorter burn duration. Overall, these results demonstrate clear benefits to NVO enabled HCCI combustion with low octane fuels.

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## Figures

Fig. 1

Schematic of the FFVA experimental setup

Fig. 2

Operational range of the baseline gasoline

Fig. 3

NVO range of the baseline gasoline

Fig. 4

Comparison of required NVO for the three test fuels

Fig. 5

Overlaid operational range of the test fuels, highlighting the 9.0 bar EMEP and peak EMEP cases

Fig. 6

Comparison of IMEPg for sweeps at 9.0 bar EMEP

Fig. 7

Cylinder pressure trace for the most advanced cases at 9.0 bar EMEP

Fig. 8

Comparing fuel/air (φ) and fuel/charge (φ′) equivalence ratio with thermal efficiency

Fig. 9

Heat release and inferred average cylinder temperature for the most advanced cases at 9.0 bar EMEP

Fig. 10

Heat release and inferred average cylinder temperature at the most retarded phasing at the highest EMEP

Fig. 11

Decreasing burn duration with lower octane fuels at 9 bar EMEP

Fig. 12

Comparison of burn duration at peak load sweeps for the three fuels

Fig. 13

Comparison of the 10–90 burn duration to CA50 and CA90 at 9.0 bar EMEP (lower graph) and peak load (upper graph—9.8 bar for Iso-octane, 10.0 bar for NH40) EMEP for iso-octane and NH40

Fig. 14

Estimated oxygen and residual gas mass fractions for the NVO sweep at 9 bar EMEP

Fig. 15

Normalized HRR of the highest IMEPg points at 9 bar EMEP

Fig. 16

Rescaled HRR to highlight ITHR for NH40 at 9 bar EMEP

Fig. 17

Normalized HRR of the highest IMEPg points at the highest EMEP for three fuels

Fig. 18

Rescaled HRR to highlight ITHR for NH40 at peak IMEPg and EMEP

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