Direct Injection Engines & Soot: What Does The Research Say?

http://www.sciencedirect.com/science/article/pii/S0306261914002608

Part-load particulate matter from a GDI engine and the connection with combustion characteristics
F. Bonatestaa, E. Chiappettaa, A. La Roccab

Highlights

• Engine-out soot and combustion data are taken from a modern GDI engine at part-load.
• Greatest soot mass is emitted in the higher load-lower speed range.
• Highest soot numbers are emitted, with size 23–40 nm, in the upper part-load range.
• Soot number concentration correlates linearly with rapid burning duration.
• Soot number concentration also correlates with unburned gas temperature.

Abstract

The Gasoline Direct Injection engines are an important source of ultra-fine particulate matter. Significant research effort is still required as improved understanding of soot formation is critical in considering further development or adoption of new technologies. Experimental measurements of engine-out soot emissions have been taken from a modern Euro IV GDI engine at part-load operating conditions. The engine speed and torque were varied in the range 1600–3700 rev/min, and 30–120 Nm, respectively. The engine was invariably operated in stoichiometric and homogeneous combustion mode, with fuel injection early in the intake stroke. The results indicate that for engine load in excess of 3 bar Brake Mean Effective Pressure, due to incomplete gas-phase mixture preparation, a consistent linear correlation establishes between combustion duration and soot particle number. On average, a sixfold increase in number concentration between 1.0 and 6.0 × 106 particle per cc, arises from shortening the rapid duration of 4 crank angle degrees. For engine speed in excess of 3000 rev/min and load in excess of 7 bar BMEP, this correlation appears to be superseded by the effects of spray-to-piston impingement and consequent pool-fire. Three main areas of concern have been identified within the part-load running envelope: (1) the higher load-lower speed range and (2) the mid load-mid speed range, where high nucleation rates induce copious increases of engine-out soot mass; (3) the upper part-load range where, most likely as a result of spray impingement, high levels of soot concentration (up to 10 million particles per cc) are emitted with very small size (23–40 nm).

Keywords
Gasoline Direct Injection; Soot number density; Soot particle size; Mass Fraction Burned; Combustion duration

Corresponding author. Tel.: +44 1865485715.
Copyright © 2014 Elsevier Ltd. All rights reserved.
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Why might ethanol help reduce that visible soot on exhaust tips?


Size distribution, chemical composition and oxidation reactivity of particulate matter from gasoline direct injection (GDI) engine fueled with ethanol-gasoline fuel
Yueqi Luo, Lei Zhu, Junhua Fang, Zhuyue Zhuang, Chun Guan, Chen Xia, Xiaomin Xie, Zhen Huang

Highlights

• Ethanol-gasoline reduces elemental carbon in PM.
• Ethanol-gasoline increases volatile organic fraction in PM.
• Soot generated from ethanol-gasoline has higher oxidation activity.

Abstract

Ethanol-gasoline blended fuels have been widely applied in markets recently, as ethanol reduces life-cycle greenhouse gas emissions and improves anti-knock performance. However, its effects on particulate matter (PM) emissions from gasoline direct injection (GDI) engine still need further investigation. In this study, the effects of ethanol-gasoline blended fuels on particle size distributions, number concentrations, chemical composition and soot oxidation activity of GDI engine were investigated. It was found that ethanol-gasoline blended fuels increased the particle number concentration in low-load operating conditions. In higher load conditions, the ethanol-gasoline was effective for reducing the particle number concentration, indicating that the chemical benefits of ethanol become dominant, which could reduce soot precursors such as large n-alkanes and aromatics in gasoline. The volatile organic mass fraction in ethanol-gasoline particulates matter was higher than that in gasoline particulate matter because ethanol reduced the amount of soot precursors during combustion and thereby reduced the elemental carbon proportions in PM. Ethanol addition also increased the proportion of small particles, which confirmed the effects of ethanol on organic composition. Ethanol-gasoline reduced the concentrations of most PAH species, except those with small aromatic rings, e.g., naphthalene. Soot from ethanol-gasoline has lower activation energy of oxidation than that from gasoline. The results in this study indicate that ethanol-gasoline has positive effects on PM emissions control, as the soot oxidation activity is improved and the particle number concentrations are reduced at moderate and high engine loads.

Keywords
Gasoline direct injection (GDI) engine; Particulate matter (PM); Ethanol-gasoline; Organic compositions; Soot oxidation activity

Corresponding authors. Tel./fax: +86 21 34205949.
Copyright © 2015 Elsevier Ltd. All rights reserved.
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http://www.sciencedirect.com/science/article/pii/S1359431114009909

Influence of the exhaust gas turbocharger on nano-scale particulate matter emissions from a GDI spark ignition engine
Matteo Cucchi, Stephen Samuel

Highlights

• Nano-scale PM from a TGDI engine is measured with a particulate spectrometer.
• Hypothesis test proves statistically relevant differences in PM across the turbine.
• As engine load increases PM number concentrations increase across the turbine.
• Particles nucleation and agglomeration are thought to occur across the turbine.
• Hypothesis test proves turbine influence regardless of exhaust gas dilution level.

Abstract

The influence of the exhaust gas turbocharger on nano-scale Particulate Matter (PM) number emissions from a Gasoline Direct Injected (GDI) engine is investigated at fixed exhaust gas dilution ratio for a matrix of three engine speeds and four engine load operating points. Experimental repeatability is assessed by means of the Coefficient of Variation (CoV) from three independent measurements for every test point. A hypothesis test on the difference between total number count before and after the turbine shows that there are statistically relevant variations for most operating points. A reduction in PM total number count at low load is observed, and an increment at high load. It is conjectured that as fuel injection pressure and duration increase with load, a larger share of volatile particulate matter is produced, which then undergoes nucleation as the exhaust gas expands through the turbine. At the same time, the centrifugal action within the turbocharger is believed to promote particle agglomeration and growth, and fragmentation of micro-scale particles. Experiments with variable dilution ratio at a fixed engine test point show that changes in dilution ratio affect repeatability of the emissions measurements only marginally. Yet, a hypothesis test on the variation of total number count with dilution shows that PM number counts are systematically affected by changes in dilution ratio. Furthermore, a hypothesis test also shows that the impact of the turbocharger on total number emissions is statistically relevant regardless of the dilution ratio adopted.

Graphical abstract
1-s2.0-S1359431114009909-fx1.jpg


Keywords
Particulate matter number emissions; Turbocharger; Gasoline direct-injection engine; Differential mobility spectrometer

Corresponding author. Faculty of Technology, Design & Environment, Department of Mechanical Engineering and Mathematical Sciences, Oxford Brookes University, Wheatley Campus, OX33 1HX, UK. Tel.: + 44 1865 483513.
Copyright © 2014 Elsevier Ltd. All rights reserved.
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