Engine Emissions: Pollutant Formation and Measurement

In recent years, emissions from transportation engines have been studied widely because of the contribution of such engines to atmospheric pollution. During this period the amounts of pollutants emitted, the mechanism of their formation, and means of controlling emissions have been investigated in industrial and government laboratories, as well as at universities. The results of these investigations have generally been published as individual articles in journals, transactions, meeting proceedings, and, frequently, in company reports. This proliferation of technical information makes it difficult for workers in the field to keep abreast of all developments. For this reason, the editors felt the need for a book which would survey the existing state of knowledge in wide, albeit selected areas, and would provide a guide to the relevant literature. This book is intended to fulfill this function. It is recognized that all aspects of transportation engine emissions cannot be explored in a single volume. In this book attention is focused primarily on sources and mechanisms of emission formation within the combustion process, and on measurement techniques. Beyond this objective, no re­ strictions were placed on the authors. Within the framework of the general theme each author has been free to treat his subject as he saw fit. The editors have not strived to replace by uniformity the highly personal and attractive divergences of style. Considerable efforts were made, however, to ensure clarity and minimum overlap between the chapters.

1. Engine Exhaust Emissions.- I. Introduction.- II. When Is an Emittant a Pollutant?.- A. Unburned Hydrocarbons.- B. Carbon Monoxide.- C. Oxides of Nitrogen.- D. Sulfur Dioxide.- E. Particulates.- III. Formation of Pollutants.- A. Carbon Monoxide.- B. Nitric Oxide.- C. Hydrocarbons.- D. Particulates.- E. Odor.- IV. Transient Operation — Engines.- A. Carbureted Spark Ignition.- B. Port Injection Spark Ignition.- C. Cylinder Injection Spark Ignition’.- D. Diesel Engine — Naturally Aspirated.- E. Diesel Engine — Turbocharged.- F. Gas Turbines.- G. External Combustion Engines.- V. Transient Operation — System.- VI. Evaluation of Vehicle Emissions.- VII. Control Techniques.- References.- 2. The Chemistry of Spark-Ignition Engine Combustion and Emission Formation.- I. Introduction.- II. Engine Processes.- A. Inputs.- B. Physical and Chemical Processes within the Engine.- C. Energy Consideration.- D. Outputs.- III. Ultimate Fate of Engine Emissions.- IV. The Engine—A Chemical Reactor.- V. The Combustion Chamber.- A. Reactor Conditions.- B. Low Temperature Reactions.- C. High Temperature Reactions in an Engine.- VI. Exhaust System.- A. Reactor Conditions.- B. Thermal Reactions in the Exhaust System.- C. Catalytic Reactions.- VII. Systems Approach to Reactions in an Engine.- VIII. Summary.- References.- 3. Mechanism of Hydrocarbon Formation in Combustion Processes.- I. Introduction.- II. Ignition Delays in Low Molecular Weight Hydrocarbon-Oxydizer Systems.- A. Introduction.- B. Experimental Results.- C. The Prediction of Induction Times.- III. Production and Emission of Unburned Hydrocarbons.- A. Introduction.- B. Flame Quenching Phenomena.- C. Sources of Unburned Hydrocarbons in Engines.- D. Effect of Engine Variables on Hydrocarbon Emissions from Spark-Ignition Engines.- IV. Some Effects of Hydrocarbon Emissions on Man and His Environment.- A. Introduction.- B. Hydrocarbons and Photochemical Smog.- C. Hydrocarbon Emissions and Odor.- D. Polynuclear Aromatic Hydrocarbon Emissions.- References.- 4. The Kinetics of Pollutant Formation in Spark-Ignition Engines.- I. Introduction.- II. Chemical Thermodynamics of the Engine Cycle.- A. Chemical Equilibrium.- B. The Role of Chemical Kinetics.- III. Combustion of Hydrocarbon Fuel-Air Mixtures and the Approach to the Initial High-Temperature Equilibrium State.- IV. Formation of Nitric Oxide.- A. Fundamental Investigations.- B. Elementary Reactions and Rate Constants for Nitric Oxide Formation.- C. Application to the Engine Cycle.- V. Expansion and Exhaust Processes.- A. General.- B. Recombination of Atoms and Radicals.- C. Oxidation of Carbon Monoxide.- D. Nitric Oxide Decomposition.- VI. The Effect of Pressure Oscillations on Nitric Oxide Kinetics.- References.- 5. Particulate Emission from Spark-Ignition Engines.- I. Introduction.- II. Measurement Techniques.- A. Particulates Collected from Outside the Exhaust System.- B. Particulate Sampling from the Exhaust System.- C. Test Procedures for Particulate Emissions.- III. Physical Characteristics of Particulates.- A. Total Particulate Matter Emitted.- B. Shape and Size Distribution of Particulates.- IV. Chemical Composition of Particulates.- A. Lead Content of Particulates.- B. Chemical Composition of Particulates.- V. Concluding Remarks.- References.- 6. Diesel Engines Combustion and Emissions.- I. Introduction.- II. Diesel Ignition and Combustion.- A. Preignition Processes.- B. Preignition Chemical Reactions.- III. Direct-Injection Engines.- A. Fuel Evaporation.- B. Fuel-Air Distribution in the Spray.- C. A Model for Combustion and Emission Formation in Direct Injection Engines.- D. Heat Release Rates in Direct Injection Engines.- E. Effect of Some Design and Operating Variables on Direct Injection Engine Emissions.- IV. The M-System.- V. Indirect Injection Engines.- A. Effect of Design and Operating Variables.- VI. Comparison Between the Emission Characteristics of Some Transportation Engines.- A. Diesel Engines.- B. Diesel and Gasoline Engines.- VII. NO Emission Control.- A. Injection Training.- B. Water Addition.- C. Exhaust-Gas Recirculation.- VIII. Concluding Remarks.- References.- 7. Diffusion and Fallout of Pollutants Emitted by Aircraft Engines.- I. Introduction.- II. Identification of Sources.- III. Diffusion and Fallout.- A. Cruising.- IV. Chemical and Physical Conversions.- V. Plume Axis from a Stack.- A. Momentum Rise.- B. Buoyancy Rise.- C. Buoyancy and Temperature Gradient.- D. Combined Relation.- VI. Plume Paths from Aircraft.- VII. Wing-Tip Vortices.- VIII. Plume Visibility.- IX. Concluding Remarks.- Notation.- References.- 8. Instrumentation and Techniques for Measuring Emissions.- I. Methods for Measuring Pollutants.- A. Terms of Expression.- B. Instrumental.- C. Wet Chemistry for Aldehyde Measurement.- II. Automotive Emissions Measurement.- A. Sampling Methods.- B. Quantifying Emissions.- C. Test Procedures.- III. Measurement of Emissions from Diesel and Turbine Engines.- A. Carbon Monoxide and Carbon Dioxide by NDIR.- B. Hydrocarbon by FID.- C. Oxides of Nitrogen.- References.- 9. Direct-Sampling Studies of Combustion Processes.- I. Introduction.- II. A Simplified Model of Molecular-Beam Sampling.- III. Boundary-Layer Considerations.- IV. Chemical Relaxations.- V. Species Condensations.- VI. Skimmer Interference.- VII. Mass Separations.- VIII. Background Scattering.- IX. Mass-Spectra Interpretations.- X. Preliminary Applications.- References.