Tham khảo tài liệu 'smog - a report to the people episode 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | the differences in emissions between EQL Strategy 1 and the present strategy Figures 3 4 and 10 . Conversions have begun for car and truck fleets which typically burn larger amounts of fuel than the average vehicles and arc alĩcaủy being attracted by the economic benefits of gaseous fuels. Since fleet vehicles burn more gasoline per vehicle the number of vehicles that would have to be converted to reduce gasoline consumption by one-third is actually somewhat less than one-third. The emissions figures do not show the full potential air quality benefits of burning gaseous fuels instead of gasoline. Unburned hydrocarbons in the exhausts of natural gas and propane vehicles have been found to be less photochemically reactive than those in gasoline exhausts. The hydrocarbons in gaseous fuels react so slowly with sunlight that they play almost no role in the formation of smog. Present vehicle emission standards do not distinguish between high and low reactivity hydrocarbons so that the natural-gas or propane-driven vehicle which meets or approaches standards is really much cleaner than a gasoline-driven vehicle with similar emission characteristics. Unburned propane hydrocarbons are only about half as reactive as those contained in gasoline and natural gas only about one-fifth as reactive. 16 B. Vacuum Spark Advance Disconnect VSAD The vacuum spark advance disconnect is a retrofit device which can be installed in all used cars up to and including 1970. It disconnects the vacuum spark advance except when a thermostatic switch senses that the car is tending to overheat. In that case the advance is reconnected until the engine cools See Section II for additional discussion. The effects of the VSAD on emissions is summarized in Table 4. The most important effect is the reduction by almost half in oxides nitrogen from 1966-1970 vehicles which characteristically emit 6 grams per mile. The retrofit also provides some reduction in the hydrocarbon emissions but almost
