PROPER maintenance and engine design can do much to reduce exhaust-gas hydrocarbons, the authors say. This conclusion is based on mass spectrometer analyses of engine exhaust from 163 passenger cars, most of them customer-owned, and 8 public-transit coaches, operated at idle, part throttle, and simulated deceleration.
Mixture ratio proved the most important engine-fuel variable affecting hydrocarbon losses at idle; thus the V-8 engine, idling best on a leaner mixture, has lowest hydrocarbon losses.
Manifold vacuum had the most effect during simulated deceleration. Since this depends on engine speed, automatic transmissions and the new lower rear-axle ratios are helpful.
None of the engine-fuel variables tested had any effect at part throttle. Type of fuel and engine type (gasoline, diesel, or LPC) showed no significant influence on hydrocarbon content throughout the tests.
Discussion of this paper begins on p. 618.