290 Diesel Technology Copyright Goodheart-Willcox Co., Inc. Clean silencers operate with less restriction. More impor- tantly, if not drained away, condensed water could react with the products of combustion, forming acids which would quickly corrode system components. To reduce heat transfer within the engine room, both the silencers and piping are insulated. The insulation can also help to reduce noise. Silencers may not be required on some turbo- charged engines due to the silencing effect of the turbo- charger. The same is true for spark arresters, but local regulations may dictate the use of one of the above in all applications. To dispose of heat radiated by exhaust pipes, sheet metal ducts are sometimes provided for the exhaust pipe with an inch or two spacing between the duct and pipe. This will provide a chimney effect and help carry away a portion of the heat. Water-cooled exhaust manifolds and pipes are used particularly in the case of marine installa- tions. Water-cooled exhaust systems are used in some industrial applications. In such cases, coolant in the closed system is recirculated. Heat can also be a problem in mobile construction equipment. The turbo and exhaust system on a diesel engine operates at extremely high temperatures, in excess of 1000°F (538°C). When running hard, pulling grades, or towing a vehicle, these temperatures increase to where the exhaust may actually glow red hot. A thermal insulation blanket kit, like the one shown in Figure 13-20, will con- tain this heat within the system, forcing it to exit the tail- pipe or outlet pipe. There are some instances when the exhaust system’s heat can be put to use. The silencer used in stationary die- sels, in addition to operating as a noise reducer, may also operate a heat recovery unit to provide heat for other plant operations, Figure 13-21. After exhaust gas enters the heat recovery silencer, it travels through a perforated tube and two silencing chambers. It then reverses its path and goes through the same silencing chamber for maximum noise reduction. It also transfers substantial heat energy to the inner body. This core section is a critical part of improving the heat transfer capability. In V-engines used in industrial and marine applica- tions, separate exhaust systems are usually provided for each bank of cylinders. Two manifold branches should not be brought together in a single pipe with a T-connection, as this leads to pulses of exhaust from one bank interfering with exhaust from the other. Extremely high back pressure may develop. Exhaust Piping Total system back pressure is greater than that of the muf- fler alone. In addition to muffler restriction, every bend and joint in the exhaust system adds resistance to exhaust flow. While truck builders would ideally prefer to install short, straight pipes with a minimum of bends and clamps, most truck exhaust systems must accommodate frame rails, battery boxes, air dryers, fuel tanks, cab mounts, and dozens of other components. The resulting pipe routing is almost always a compromise between what the engine ideally needs and what will fit on the truck. The exhaust systems of mobile diesel applications can be grouped into two main types. Figure 13-19. Silencers and exhaust pipe covered with insulation to reduce heat. (Advanced Thermal Products) Figure 13-20. Insulation kit applied to a mobile diesel exhaust system. (Advanced Thermal Products)