Two stroke engine starting

•The direct admission of high pressure air, into the cylinders of the engine for starting, is used for larger engines, where the large masses and inertia do not make external cranking practicable.

•  Each unit has a separate starting valve, and there is a period of overlap, so that even if anyone unit starting valve should not operate, the engine can still be started.

Draw back of comp.air starting

•large quantity of compressed air is injected into each unit, and if the fuel injector were to leak, there is a chance of premature explosion, leading to excessive pressure rise and possible engine damage.

•To take care of this, cylinder relief valve are fitted.

•There need to be a minimum number of units, ( 4), to enable the engine to be started from any position.

•Moisture in the starting air will enter the unit, which could create corrosion problems

 Comp.air starting

•Starting air can be supplied from TDC till the opening of the exhaust valve / exhaust ports, in theory.

•In practice, the valve is timed to open a little before TDC, since there is always a period of 'lag', between the opening of the valve, and the actual action of the air, which must fill the cylinder first, before its turning effect is felt on the piston

•Inverse cams are preferred. It becomes easier to take the rollers off the cam,

•once the engine has picked up speed and there is no possibility of stuck pilot valves or broken springs causing any cylinder air starting valve to remain in the open position.

 comp.air starting/safety devices

•. Non-return valve in the Starting Air line, closest to the Main engine.

•. Relief valve in each Cylinder head of the Main Engine.

•. Means to prevent Starting Air admission to a unit which is already firing.