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Research Papers: Internal Combustion Engines

# Comparison of Filter Smoke Number and Elemental Carbon Mass From Partially Premixed Low Temperature Combustion in a Direct-Injection Diesel Engine

[+] Author and Article Information
William F. Northrop, Stanislav V. Bohac, Dennis N. Assanis

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109

Jo-Yu Chin

Department of Environmental Health Sciences, University of Michigan, Ann Arbor, MI 48109

J. Eng. Gas Turbines Power 133(10), 102804 (May 04, 2011) (6 pages) doi:10.1115/1.4002918 History: Received October 11, 2010; Revised October 13, 2010; Published May 04, 2011; Online May 04, 2011

## Abstract

Partially premixed low temperature combustion (LTC) is an established advanced engine strategy that enables the simultaneous reduction of soot and $NOx$ emissions in diesel engines. Measuring extremely low levels of soot emissions achievable with LTC modes using a filter smoke meter requires large sample volumes and repeated measurements to achieve the desired data precision and accuracy. Even taking such measures, doubt exists as to whether filter smoke number (FSN) accurately represents the actual smoke emissions emitted from such low soot conditions. The use of alternative fuels such as biodiesel also compounds efforts to accurately report soot emissions since the reflectivity of high levels of organic matter found on the particulate matter collected may result in erroneous readings from the optical detector. Using FSN, it is desired to report mass emissions of soot using empirical correlations derived for use with petroleum diesel fuels and conventional modes of combustion. The work presented in this paper compares the experimental results of well known formulas for calculating the mass of soot using FSN and the elemental carbon mass using thermal optical analysis (TOA) over a range of operating conditions and fuels from a four-cylinder direct-injection passenger car diesel engine. The data show that the mass of soot emitted by the engine can be accurately predicted with the smoke meter method utilizing a 3000 ml sample volume over a range of FSN from 0.02 to 1.5. Soot mass exhaust concentration calculated from FSN using the best of the literature expressions and that from TOA taken over all conditions correlated linearly with a slope of 0.99 and $R2$ value of 0.94. A primary implication of the work is that the level of confidence in reporting the soot mass based on FSN for low soot formation regimes such as LTC is improved for both petroleum diesel and biodiesel fuels.

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## Figures

Figure 7

Linear trend for EC concentration versus soot concentration based on the correlation of Christian (12) for all data taken in this study

Figure 1

Diagram of filter smoke meter location and partial dilution tunnel sampling system where EC filter samples were loaded

Figure 2

Rate of heat release and injector current signal for two conditions tested in this study: conventional combustion at 1500 rpm, 600 kPa BMEP, diesel fuel, and 27% EGR and LTC at 1500 rpm, 400 kPa BMEP, diesel fuel, and 45% EGR

Figure 3

Filter smoke number versus emissions index of NOx for all conditions and fuels

Figure 4

Concentration of elemental carbon in the exhaust for biodiesel blends in conventional versus LTC operation

Figure 5

Smoke mass concentration in exhaust versus FSN for four literature correlations over entire practical range of FSN

Figure 6

Smoke mass concentration versus FSN, comparing four literature correlations with the data recorded in this study

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