Tham khảo tài liệu 'intro to marine engineering 2 2011 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 20 Diesei engines arrangements have low temperature air and high temperature exhaust gas passing through adjacent ports causing temperature differential problems for the liner material. Uniflow is the most efficient scavenging system but requires either an opposed piston arrangement or an exhaust valve in the cylinder head. All three systems have the ports angled to swirl the incoming air and direct it in the appropriate path. Scavenge fires Cylinder oil can collect in the scavenge space of an engine. Unburned fuel and carbon may also be blown into the scavenge space as a result of defective piston rings faulty timing a defective injector etc. A build-up of this flammable mixture presents a danger as a blow past of hot gases from the cylinder may ignite the mixture and cause a scavenge fire. A loss of engine power will result with high exhaust temperatures at the affected cylinders. The affected turbo-chargers may surge and sparks will be seen at the scavenge drains. Once a fire is detected the engine should be slowed down fuel shut off from the affected cylinders and cylinder lubrication increased. All the scavenge drains should be closed. A small fire will quickly burn out but where the fire persists the engine must be stopped. A fire extinguishing medium should then be injected through the fittings provided in the scavenge trunking. On no account should the trunking be opened up. To avoid scavenge fires occurring the engine timing and equipment maintenance should be correctly carried out. The scavenge trunking should be regularly inspected and cleaned if necessary. Where carbon or oil build up is found in the scavenge its source should be detected and the fault remedied. Scavenge drains should be regularly blown and any oil discharges investigated at the first opportunity. Fuel oil system The fuel oil system for a diesel engine can be considered in two parts the fuel supply and the fuel injection systems. Fuel supply deals with the provision of fuel oil suitable
