Diesel engines for land and marine work . two-cycle marine engines the question of scaveng-ing is one of some difficulty. A big volume of air at lowpressure has to be admitted, and it is impossible to accom-plish this by means of one valve only, when valves areemployed. In the Carels engine for large powers, fourscavenge valves are fitted to each cylinder, arranged in thecover and operated by two levers and two cams. Themethod is somewhat expensive, and to a certain extentcomplicated, and largely minimizes the advantage of sim-plicity which the two-cycle engine might otherwise claimover the fo
Diesel engines for land and marine work . two-cycle marine engines the question of scaveng-ing is one of some difficulty. A big volume of air at lowpressure has to be admitted, and it is impossible to accom-plish this by means of one valve only, when valves areemployed. In the Carels engine for large powers, fourscavenge valves are fitted to each cylinder, arranged in thecover and operated by two levers and two cams. Themethod is somewhat expensive, and to a certain extentcomplicated, and largely minimizes the advantage of sim-plicity which the two-cycle engine might otherwise claimover the four-cycle, but it ensures very efficient scavenging. In spite of the many valves necessitated by this arrange-ment, reversing is very rapidly carried out, the time takenfrom full speed ahead to full speed astern being about Q 226 DIESEL ENGINES FOR LAND AND MARINE WORK 10 seconds. The general principle of the method of revers-ing is to provide a separate ahead and astern cam side byside, both for the fuel valve and the starting valve, and. only one cam for each pair of scavenge valves. It is evidentthat as far as] the actuation of] these valves is concerned,this arrangement is sufficient if the cam shaft is turned CONSTRUCTION OF DIESEL MARINE ENGINE 227 through a certain angle relative to the crank shaft. Whenthe engine runs in the astern direction, the scavenge valveswill be opened at the correct moment for reverse running.
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