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Research Papers: Internal Combustion Engines

# Low-Temperature Combustion Within a HSDI Diesel Engine Using Multiple-Injection Strategies

[+] Author and Article Information
Tiegang Fang1

Department of Mechanical and Aerospace Engineering, North Carolina State University, 3182 Broughton Hall, Campus Box 7910, 2601 Stinson Drive, Raleigh, NC 27606tfang2@ncsu.edu

Robert E. Coverdill, Chia-Fon F. Lee, Robert A. White

Department of Mechanical Science and Engineering, University of Illinois at Urbana–Champaign, 1206 West Green Street, Urbana, IL 61801

1

Corresponding author.

J. Eng. Gas Turbines Power 131(6), 062803 (Jul 15, 2009) (8 pages) doi:10.1115/1.3093999 History: Received October 16, 2008; Revised November 16, 2008; Published July 15, 2009

## Abstract

Low-temperature compression ignition combustion employing multiple-injection strategies in an optical high-speed direct injection diesel engine was investigated. Heat release characteristics were analyzed. The whole cycle combustion process was visualized by imaging the natural flame luminosity. The $NOx$ emissions were measured in the exhaust pipe. The effects of the pilot injection timing, pilot fuel quantity, main injection timing, operating load, and injection pressure on the combustion and emissions were studied. Low-temperature combustion modes were achieved by using a small pilot injection with an injection timing much earlier than top dead center (TDC) followed by a main injection after TDC. The results were compared with conventional diesel (diffusion) combustion for comparison purposes. A premixed-combustion-dominated heat release rate pattern was seen for all the low-temperature combustion cases, while a typical diffusion flame combustion heat release rate was obtained for the conventional combustion case. A highly luminous flame was observed for the conventional combustion condition while a much less luminous flame was seen for the low-temperature combustion cases. For the higher-load and lower injection pressure cases, liquid fuel being injected into low-temperature premixed flame was observed for certain cases. Compared with the conventional diffusion combustion, simultaneous reductions in soot and $NOx$ were obtained for the low-temperature combustion mode under similar operating loads. For high-load conditions, higher $NOx$ emissions were obtained due to higher in-cylinder temperatures. However, compared with the conventional combustion case, a significant reduction in soot was achieved for the high-load conditions, which shows that increasing injection pressure greatly reduces soot emissions.

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## Figures

Figure 1

In-cylinder pressure for the 12 low-temperature combustion cases

Figure 2

Needle-lift data for the 12 low-temperature combustion cases

Figure 3

Heat release rates for the 12 low-temperature combustion cases

Figure 4

Heat release rates of the pilot injections for the 12 low-temperature combustion cases

Figure 5

Spatially integrated flame luminosity for the 12 low-temperature combustion cases

Figure 6

The variation rates of spatially integrated flame luminosity for the 12 low-temperature combustion cases

Figure 7

The FLP and NOx parameters for low-temperature combustion conditions with a multiple-injection strategy

Figure 8

Early combustion images at the end of the main injection

Figure 9

Combustion images with strong flame luminosity

Figure 10

Late cycle combustion images

Figure 11

In-cylinder pressure and heat release rate for Case 1 and the conventional combustion case

Figure 12

Cycle thermal efficiency for Cases 1–12 and the conventional combustion case

Figure 13

Combustion flame images of the conventional combustion condition

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