Abstract: The exhaust system of an internal combustion engine which includes one or several, sequential catalytic reactors is provided with a bypass channel through which some portion of the exhaust gases may be diverted. This diversion takes place whenever the gas flow rate becomes so high that the operating temperatures of one or more of the reactors would be exceeded. The gases flowing through the bypass channel are cooled prior to their reintroduction into the main exhaust pipe channel. The diversion of part of the gas stream into the bypass channel is accomplished with the aid of a control current of exhaust gas tapped off from the exhaust line and conducted back upstream to the junction of the main channel and the bypass channel. The force of this control current deviates the exhaust gases from their normal path and causes them to flow into the bypass channel.

Abstract: To test optical transmissivity of exhaust gases from internal combustion engines without requiring cleaning of confining walls of pipes or tubes, a film of liquid is caused to adhere to the inner surface of a transparent tube or pipe section by rotating the tube or pipe section so that the film will remain at the inner wall due to centrifugal force; light is transmitted transversely of the pipe section and through the exhaust gas. The liquid is preferably continually renewed by applying fresh liquid to the inside of the rotating pipe section, excess liquid being removed from an overflow ridge.