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.