TWO STROKETWO STROKE

ENGINEENGINE

TWO STROKE CYCLETWO STROKE CYCLE The two stroke cycle is completed in two strokes of The two stroke cycle is completed in two strokes of

the piston or one revolution of the crankshaft.the piston or one revolution of the crankshaft. In order to operate this cycle successfully, special In order to operate this cycle successfully, special

arrangements are required such as:-arrangements are required such as:--- The fresh air must be forced in under pressure The fresh air must be forced in under pressure and useful to cleared out exhaust gases.and useful to cleared out exhaust gases.-- Instead of valve holes, known as ‘ports’, are Instead of valve holes, known as ‘ports’, are used which are opened and closed by the used which are opened and closed by the sides sides of the piston as its moves .of the piston as its moves .

SUCTION / SCAVENGE STROKESUCTION / SCAVENGE STROKE

It begin when scavenge ports opened It begin when scavenge ports opened by the movement of the piston by the movement of the piston downward till BDC.downward till BDC.

At the time fresh air entered the At the time fresh air entered the cylinder, the remaining exhaust gas cylinder, the remaining exhaust gas were forced out from the cylinder.were forced out from the cylinder.

Fuel valve closed.Fuel valve closed.

COMPRESSION STROKECOMPRESSION STROKE

The piston move upward with fuel injector The piston move upward with fuel injector remain closed.remain closed.

When scavenge ports closed, some fresh When scavenge ports closed, some fresh air may blow out through open exhaust ports air may blow out through open exhaust ports to ensure no exhaust gas remain.to ensure no exhaust gas remain.

When exhaust ports closed, the When exhaust ports closed, the compression begin and let the temperature compression begin and let the temperature of air rise for combustion. of air rise for combustion.

POWER STROKEPOWER STROKE

Before the piston reach TDC (approximately Before the piston reach TDC (approximately 10 to 1510 to 15o o before TDC) fuel injector supplying before TDC) fuel injector supplying fuel oil in fine spray (end of operation fuel oil in fine spray (end of operation approximately 10 to 15approximately 10 to 15o o after TDC).after TDC).

The mixture ignite and due to expansion of The mixture ignite and due to expansion of the gases tend to push piston move the gases tend to push piston move downward as Power Stroke.downward as Power Stroke.

Both exhaust and scavenge ports were Both exhaust and scavenge ports were closedclosed

EXHAUST STROKEEXHAUST STROKE

The moment exhaust ports uncovered by The moment exhaust ports uncovered by the movement of the piston downward, the the movement of the piston downward, the exhaust stroke begin.exhaust stroke begin.

Exhaust gases will automatically blow off Exhaust gases will automatically blow off from the cylinder through these exhaust from the cylinder through these exhaust ports.ports.

Fuel injector remain closed. Thus the Fuel injector remain closed. Thus the moment scavenge ports opened scavenge moment scavenge ports opened scavenge stroke begin and the cycle will continue until stroke begin and the cycle will continue until the engine stopthe engine stop

TWO STROKE ADVANTAGESTWO STROKE ADVANTAGESMAIN ADVANTAGESMAIN ADVANTAGES

Compactness in relation to the power output and not Compactness in relation to the power output and not requires to increase brake mean effective pressure or the requires to increase brake mean effective pressure or the engine speed to increase rating. engine speed to increase rating.

High bmep increases the stresses on nearly all the engine High bmep increases the stresses on nearly all the engine components, with a consequently greater rate of cylinder components, with a consequently greater rate of cylinder wear, whilst the alternative of higher speed, valve flutter wear, whilst the alternative of higher speed, valve flutter may become a serious problem.may become a serious problem.

Each out-stroke being a working stroke gives more even Each out-stroke being a working stroke gives more even turning for the same number of cranks, consequently a turning for the same number of cranks, consequently a lighter flywheel may be employed.lighter flywheel may be employed.

The reversing operation of rotation is simplified since there The reversing operation of rotation is simplified since there are not to many valve gear to contend with.are not to many valve gear to contend with.

OTHER ADVANTAGESOTHER ADVANTAGES

Fewer moving parts and lower maintenanceFewer moving parts and lower maintenance Lower specific fuel consumptionLower specific fuel consumption No gear lossNo gear loss Simplicity in constructionSimplicity in construction Longer life timesLonger life times Higher reliability (product)Higher reliability (product) Low lubrication oil consumptionLow lubrication oil consumption Better ability to burn low quality fuel oilBetter ability to burn low quality fuel oil

MAIN ADVANTAGESMAIN ADVANTAGES

Good volumetric efficiency, good combustion Good volumetric efficiency, good combustion characteristic and positive exhaust scavenging.characteristic and positive exhaust scavenging.

The thermal and mechanical efficiencies are The thermal and mechanical efficiencies are slightly better than those of two stroke engine.slightly better than those of two stroke engine.

In this type of engine only half the quantity of the In this type of engine only half the quantity of the heat generated in the cylinders has to be dealt heat generated in the cylinders has to be dealt with a given time, so that efficient lubrication of the with a given time, so that efficient lubrication of the piston and cooling of the cylinder is more easily piston and cooling of the cylinder is more easily accomplished.accomplished.

FOUR STROKE ADVANTAGESFOUR STROKE ADVANTAGES

Lower initial cost for equivalent powerLower initial cost for equivalent power Ease of installationEase of installation Lower weight per powerLower weight per power Saving in weight and engine room lengthSaving in weight and engine room length Increase cargo capacityIncrease cargo capacity Free choice of propeller speed through Free choice of propeller speed through

gearinggearing Suitable for electrical power take offSuitable for electrical power take off

OTHER ADVANTAGESOTHER ADVANTAGES