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Variable Cam Timing as an Emission Control Tool
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Sector:
Event:
National West Coast Meeting
Language:
English
Abstract
Automatic variation of internal combustion engine valve timing in response to load and speed is an effective technique for reducing emission of oxides of nitrogen and unburned hydrocarbons. The variation employed is cam advance, which causes part of the exhaust gases normally expelled near the end of the exhaust stroke to be retained and mixed with the fresh air-fuel mixture during the following inlet stroke. Part of the unburned hydrocarbons normally emitted are contained in these recirculated end-of-stroke gases, and are oxidized further by re-exposure to combustion. The peak flame temperature is reduced by the diluent, and formation of oxides of nitrogen is suppressed.
A prototype vehicle equipped with an automatic cam advance system shows that emissions measured by the Federal Test Procedure are reduced by the following amounts: nitric oxide 64%, unburned hydrocarbons 32%, and carbon monoxide 16.5%.
Only minimal changes in vehicle operating characteristics are caused, and potential durability is good since the existing engine valves and pistons are used to handle the recirculated exhaust. The cylinder-to-cylinder distribution of the diluent is inherently uniform, and the amount of recirculation is repeatable.
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Authors
Topic
Citation
Meacham, G., "Variable Cam Timing as an Emission Control Tool," SAE Technical Paper 700673, 1970, https://doi.org/10.4271/700673.Also In
References
- Newhall H. K. “Control of Nitrogen Oxides by Exhaust Recirculation.” SAE Transactions 76 1967 paper 670495
- Nicholls J. E. El-Messiri I. A. Newhall H. K. “Inlet Manifold Water Injection for Control of Nitrogen Oxides-Theory and Experiment.” Paper 690018 SAE Automotive Engineering Congress Detroit January 1969
- Glass W. Russell F. R. Wade D. T. Hollabaugh D. M. “Evaluation of Exhaust Recirculation for Control of Nitrogen Oxides Emissions.” Paper 700146 SAE Automotive Engineering Congress Detroit January 1970
- Daniel W. A. “Engine Variable Effects on Exhaust Hydrocarbon Formations (Single Cylinder Engine Study with Propane as Fuel).” Paper 670124 SAE Automotive Engineering Congress Detroit January 1967