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Research Papers: Internal Combustion Engines

# An Experimental and Modeling Study of HCCI Combustion Using $n$-Heptane

[+] Author and Article Information
Hongsheng Guo, W. Stuart Neill, Wally Chippior

Hailin Li

West Virginia University, P.O. Box 6106, Morgantown, WV, 26506

Joshua D. Taylor

National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401

J. Eng. Gas Turbines Power 132(2), 022801 (Oct 15, 2009) (10 pages) doi:10.1115/1.3124667 History: Received November 28, 2006; Revised August 07, 2008; Published October 15, 2009

## Abstract

Homogeneous charge compression ignition (HCCI) is an advanced low-temperature combustion technology being considered for internal combustion engines due to its potential for high fuel conversion efficiency and extremely low emissions of particulate matter and oxides of nitrogen $(NOx)$. In its simplest form, HCCI combustion involves the auto-ignition of a homogeneous mixture of fuel, air, and diluents at low to moderate temperatures and high pressure. Previous research has indicated that fuel chemistry has a strong impact on HCCI combustion. This paper reports the preliminary results of an experimental and modeling study of HCCI combustion using $n$-heptane, a volatile hydrocarbon with well known fuel chemistry. A Co-operative Fuel Research (CFR) engine was modified by the addition of a port fuel injection system to produce a homogeneous fuel-air mixture in the intake manifold, which contributed to a stable and repeatable HCCI combustion process. Detailed experiments were performed to explore the effects of critical engine parameters such as intake temperature, compression ratio, air/fuel ratio, engine speed, turbocharging, and intake mixture throttling on HCCI combustion. The influence of these parameters on the phasing of the low-temperature reaction, main combustion stage, and negative temperature coefficient delay period are presented and discussed. A single-zone numerical simulation with detailed fuel chemistry was developed and validated. The simulations show good agreement with the experimental data and capture important combustion phase trends as engine parameters are varied.

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## Figures

Figure 6

Effect of engine speed on NTC delay: CR=10.0, Tin,air=40°C, Pin=95 kPa, Pexh=104 kPa, fuel: n-heptane, AFR=50.

Figure 7

(a) Cylinder pressure; (b) heat release rate. Effect of air-fuel ratio on HCCI combustion: CR=10.0, Tin,air=40°C, Pin=95 kPa, Pexh=104 kPa, N=900 rpm.

Figure 8

Effect of air-fuel ratio on NTC delay: CR=10.0, Tin,air=40°C, Pin=95 kPa, Pexh=104 kPa, N=900 rpm

Figure 9

(a) Cylinder pressure; (b) heat release rate. Effect of turbocharging on HCCI combustion: CR=10, Tin,air=40°C, AFR=60.0, N=900 rpm.

Figure 13

(a) Cylinder pressure; (b) heat release rate. Effect of compression ratio on HCCI combustion: Tin,air=30°C, Pin=95 kPa, Pexh=104 kPa, N=900 rpm, AFR=50.

Figure 14

Effect of compression ratio on NTC delay: Tin,air=30°C, Pin=95 kPa, Pexh=104 kPa, N=900 rpm, AFR=50

Figure 15

(a) Cylinder pressure; (b) heat release rate. Effect of intake air throttling on HCCI combustion at constant intake fuel flow rate: N=900 rpm, CR=10.0, Tin,air=40°C, Pexh=104 kPa, ṁfuel=0.273 kg/h, AFR=20–60.

Figure 1

Schematic of HCCI engine setup

Figure 2

Variation of effective intake mixture temperature with intake air temperature: N=900 rpm, CR=10.0, Pin=95 kPa, Pexh=104 kPa, AFR=50

Figure 3

Ignition delay of n-heptane at moderate and high pressure for both lean and stoichiometric mixtures. Experimental data were obtained from Ref. 23.

Figure 4

Variation of (a) cylinder pressure (HCCI and motoring), (b) cumulative heat release, and (c) heat release rate with crank angle; CR=10, Tin=30°C, AFR=50, Pin=95 kPa

Figure 5

Effect of engine speed on (a) cylinder pressure and (b) heat release rate: CR=10.0, AFR=50, Tin,air=40°C, Pin=95 kPa, Pexh=104 kPa

Figure 10

Effect of turbocharging on NTC delay: CR=10, Tin,air=40°C, AFR=60.0, N=900 rpm

Figure 11

(a) Cylinder pressure; (b) heat release rate. Effect of intake air temperature on HCCI combustion: N=900 rpm, CR=10.0, Pin=95 kPa, Pexh=104 kPa, AFR=50.

Figure 12

Effect of intake air temperature on NTC delay: N=900 rpm, CR=10.0, Pin=95 kPa, Pexh=104 kPa, AFR=50

Figure 20

Comparison of the predicted CA50 with those determined experimentally over a range of intake pressures. Operating condition is the same as in Fig. 9.

Figure 16

Effect of throttling intake air on total heat release and indicated specific fuel consumption when intake fuel flow rate was kept constant: N=900 rpm, CR=10.0, Tin,air=40°C, Pexh=104 kPa, ṁfuel=0.273 kg/h, AFR=20–60

Figure 17

Comparison of predicted (a) cylinder pressure, (b) heat release rate, and (c) cumulative heat release with experimental data: CR=10, Tin,air=30°C, AFR=50, Pin=95 kPa

Figure 18

Comparison of the predicted CA50 with those determined experimentally over a range of compression ratios. Operating condition is the same as Fig. 1.

Figure 19

Comparison of the predicted CA50 with those determined experimentally over a range of engine speeds. Operating condition is the same as in Fig. 5.

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