Handbook of Air Pollution from Internal Combustion Engines

Pollutant Formation and Control

Eran Sher

• Publisher: Academic Press
• Year: 1998
• Print ISBN:
  9780126398557
• eBook ISBN:
  9780080532752
• Topic: Technology & Engineering
• Subtopic: Environmental Management
• Index: Technology & Engineering

This handbook is an important and valuable source for engineers and researchers in the area of internal combustion engines pollution control. It provides an excellent updated review of available knowledge in this field and furnishes essential and useful information on air pollution constituents, mechanisms of formation, control technologies, effects of engine design, effects of operation conditions, and effects of fuel formulation and additives. The text is rich in explanatory diagrams, figures and tables, and includes a considerable number of references. - An important resource for engineers and researchers in the area of internal combustion engines and pollution control - Presents and excellent updated review of the available knowledge in this area - Written by 23 experts - Provides over 700 references and more than 500 explanatory diagrams, figures and tables

Part I

Overview

Chapter 1

Motor Vehicle Emissions Control: Past Achievements, Future Prospects^♦

John B. Heywood Sun Jae Professor of Mechanical Engineering, Director, Sloan Automotive Laboratory, Massachusetts Institute of Technology, Massachusetts, USA

1.1 Synopsis 4

1.2 Introduction 4

1.3 Motor Vehicles and Air Pollution 5

1.4 The Science of Pollutant Formation and Control 9

1.5 Effectiveness of Current Emission Control Technology 15

1.6 Direct-Injection Engines, Two-Strokes, and Diesels 17

1.7 Future Prospects 20

References 23

1.1 SYNOPSIS

Motor vehicles—cars, trucks, and buses—are a major source of air pollution. For 35 years we have been both learning about the problem and attempting to control vehicle emissions. In this introduction, we trace the history of our efforts to understand this important environmental issue and to find effective solutions, as well as look ahead to the future. While steady progress has been made and effective technology, such as engine controls, exhaust catalysts, and improved fuels, has been developed at the individual vehicle level, the full resolution of this problem still escapes us. Growth in vehicle use and the failure of the emission controls in a small but significant fraction of vehicles have offset a substantial part of the anticipated gains. Looking to the future, are prospects for effective emissions control better? Yes, improved fuel injection, sensors and controls, and catalyst technologies are being developed, more effective inspection programs are being implemented, and alternative fuels may play some role. However, growth in vehicle use will continue to present a major environmental challenge to both automotive engineers and regulators.

1.2 INTRODUCTION

In the 1950s through studies in Los Angeles, it became clear that emissions from automobiles were a major contributor to urban air pollution. This smog, formed in the atmosphere as a result of complex photochemistry between hydrocarbons—often called volatile organic compounds (HC or VOC), and oxides of nitrogen (NO_x)—on warm spring, summer, and fall days, results in high ambient levels of ozone and other oxidants. In addition, automobiles are the dominant source of carbon monoxide (CO) and of lead. It is not just cars: Light trucks, heavy trucks, and off-road vehicles also contribute significantly. So do stationary combustion systems. Even natural (i.e., biogenic) hydrocarbon emissions are important.

Starting in the late 1960s, vehicle emissions in the developed world have been regulated with increasing strictness. More recently, the fuels that the spark-ignition and diesel engines in these vehicles use (i.e., gasoline/petrol and diesel) have been or are about to be subject to more stringent constraints with the intent of further reducing emissions. This introduction traces the history of our efforts to understand this important environmental issue and to find effective solutions. We have made steady progress on improving urban air quality, yet the full resolution of the problem still eludes us. Looking at this problem of motor vehicles and air pollution from a broader perspective, there are several important questions. Just what is the problem? What have we done so far? Why is it proving to be such a difficult problem to solve, both fundamentally and in practice? What are the prospects for future improvements?

It has been my good fortune that the evolution of this problem and our attempts to resolve it have coincided with my own professional career. There is tremendous excitement and satisfaction in working on a new research problem with the opportunity to contribute to the development of technology that will help to resolve the problem. Over the past 30 years we have learned a great deal more about the internal combustion engine, the prime mover that is so ubiquitous and important to our modern lives. Whether it is a blessing or a curse is not the issue here: The internal combustion engine exists, is used worldwide in very large numbers, and that pattern will continue into the future. However, the internal combustion engine does need to become steadily more environmentally friendly.

1.3 MOTOR VEHICLES AND AIR POLLUTION

In the United States, cars, trucks, and off-road vehicles are currently estimated to be responsible for about 40 percent to 50 percent of the HC or VOC emissions, 50 percent of the NO_x emissions, and 80 percent to 90 percent of the CO emissions in urban areas. The relative contributions in other parts of the developed world such as in Europe and Japan are similar. A large fraction of these emissions still comes from cars and light trucks with spark-ignition engines, though the relative importance of NO_x and particulates from diesel engines is rising. Over the past decade (1982–1991) in the aggregate, CO and VOC emissions from mobile sources have decreased about 40 percent and NO_x emissions by 25 percent despite substantial growth in vehicle miles traveled. However, it is the changes in seasonal emissions—winter for CO and summer for VOC and NO_x—that matter, and significant differences exist from one urban area to another. It also has become clear that photochemical smog with its high ozone levels is now a large-scale regional problem transported by the prevailing winds, with ozone concentrations in rural areas often reaching about half the urban peaks. Air quality measurements in the United States show that urban ozone levels have decreased by about 12 percent over the 1984–1993 decade, and incidents when the ozone National Ambient Air Quality Standard is exceeded have decreased by 60 percent. Ambient carbon monoxide levels have decreased by about 40 percent over the same period. These improvements have come primarily from the engine technology changes that emissions regulations have demanded.

Auto emissions control has a long history. Exhaust emission standards for new cars were first set in 1968 (1965 in California), after which the standards for exhaust emissions became steadily stricter every couple of years until the early 1980s. Much more stringent standards for the 1990s and beyond have now been established, especially in the United States and Europe (Table 1.1). The strategy adopted to minimize smog was major reductions in unburned HC emissions with lesser reductions in NO_x. The strategy was chosen in part from our assessment of how the photochemical smog chemistry responds to changes in HCs and NO_x as well as from the technical feasibility of reducing HCs relative to NO_x. Emissions standards for engines in large vehicles (gasoline-fueled and diesel) have steadily become stricter too, though lagging in time.

Table 1.1

Future U.S. Light-Duty Vehicle Exhaust Emission Standards¹

Standard type	NMOG	CO	NOx	HCHO
Precontrol (1966)	10.6	84 Federal	4.1
Tier I (1994)	0.25	3.4	0.4
Tier II (2003)	0.125	1.7 California	0.2
Conventional vehicles (1993)	0.25	3.4	0.4
TLEVs (1994)	0.125	3.4	0.4	0.015
LEVs (1997)	0.04	1.7	0.2	0.015
Ultra LEVs (1997)	0.04	1.7	0.2	0.008

NMOG, nonmethane organic gas (sum of nonoxygenated and oxygenated HCs). Standards are for five years or 50,000 miles. Transitional low-emission vehicles (TLEVs). Low-emission vehicles (LEVs).

Let us focus first on the emissions control issues of automobiles with gasoline-fueled spark-ignition (SI) engines. While diesel trucks are an important contributor to air pollution, and diesel cars are growing to be a significant fraction of new car sales in Europe due to high fuel prices and their higher efficiency, the spark-ignition engine still dominates the motor vehicle emissions problem. To provide some perspective on past and present emissions levels, Table 1.2 gives typical numbers for the fuel consumed, the engine emission...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Dedication
• List of Contributors
• Acknowledgments
• Part I: Overview
• Part II: Global Aspects
• Part III: Spark-Ignition Engines
• Part IV: Compression-Ignition Engines
• Part V: Two-Stroke Engines
• Part VI: Spark-Ignition Engines
• Index