Diesel Engine Starting and Reversing

Small Engine Starting Systems Small diesel engine starting systems use a small high torque motor to overcome the static friction of the engine. The motor engages the flywheel and turns the engine over.

Small Engine Starting Systems Electric Motors – A series wound DC motor is used because of the high starting torque it produces. The source of power is a lead acid battery. The motor engages the engine through the use of a pinion on the starting motor from the a gear on the engine flywheel.

Small Engine Starting Systems Hydraulic motors – use hydraulic energy which is stored in accumulators. The high pressure cylinders are precharged with nitrogen. The nitrogen and oil are separated by a piston. A pump is provided to keep the system pressure up The system pressure can be as high as 3000 psi

Small Engine Starting Systems Air Motor – This system uses a air motor with air supplied from compressed air tanks. A compressor is used to pump up the tanks.

Starting Air Systems Direct air starting systems are used on large diesel engines. Ship service generators are usually the smallest engines that use this system. The starting air valve is located on the cylinder head. Air is admitted a little past TDC on the power stroke.

Starting Air Systems This is because all the valves are closed and the ports are covered. Rotating the engine up to speed in the correct direction. A minimum of five cylinders are required to have starting valves in a four stroke cycle diesel engine. A minimum of three cylinders are required to have air start valves on a two stroke engine.

Starting Air Systems High pressure compressors are multistage, water-cooled. There are at least two main compressors. A small electrically driven air compressor can be run by the emergency diesel generator during cold start-up. The air storage tanks or air receivers are large, high pressure vessels are subject to regulations governing unfired pressure vessels by the USCG

Starting Air System Storage Tanks Pressure range is 500 to 600 psi. The receiver must hold twelve starts without the use of the compressor for a direct drive main propulsion engine. For a marine engine with a controllable reversible pitch propeller the receiver must be able to hold six starts. Rule of Thumb: The physical volume of the storage tanks is thirty times the physical volume of one engine cylinder.

Starting Air System Storage Tanks The receivers must have a relief valve since they are an unfired pressure vessel. A separate valved line to the tank and a separate valved line from the tank must be provided to ensure moisture does not get into the downstream components.

Reversing Main Propulsion Engine Fuel to the injectors must stop. Starting air is admitted to the cylinders to stop the engine. The timing of the engine must be changed Reversing the direction of the cam shaft. Shifting the cam shaft axially engaging a set of reversing cams

Reversing Main Propulsion Engine The main starting air valve is activated, putting air to the cylinder which the piston is in the reverse power position. Once the engine is rotating in the astern direction fuel is admitted to the fuel injectors.