Text 11

Why 2-Stroke Engines Are Used More Commonly

Than 4-Stroke on Ships?

When a ship is being constructed in a shipyard, the most important machinery that is to be selected is the main propulsion machinery. Both 2 stroke and 4 stroke engines are widely available in the market but for large ocean going merchant vessel, a 2 stroke engine is more commonly used as main engine and has much better market.

Even with wide variety of advantages that 4 stroke engine offers like compact size of plant, much more RPM or speed etc, a 2 stroke engine outshines with few but vital advantages.

Some of the important reasons why 2 stroke engines are more popular than 4 stroke engines as main propulsion engine on ships

Fuel Selection: The fuel prices have gone sky high and better grade fuel is adding higher costs to vessel operation. A two stroke engine can burn low grade fuel oil and hence reduce running cost of the ship.

Efficiency: The thermal and engine efficiency of 2 stroke engine is much better than that of a 4 stroke engine.

Power: Most of the 2 stroke engines are now large stroke engines that produce more power. Hence they have high power to weight ration as compare to 4 stroke engine.

More Cargo: Ship can carry more weight and hence more cargo with 2 stroke engines because of high power to weight ratio.

Reliability: Two stroke engines are more reliable in operation as compare to 4 stroke engine.

Less Maintenance: The maintenance requirement of two stroke engine is much lesser than 4 stroke engine.

Direction control: Direct starting and reversing is easier with two stroke engine.

No reduction attachments: As two stroke engines are low speed engine, there are no requirement of reduction gear or speed reduction arrangement as required for high speed four stroke engine.

However, the ease-of-manoeuvring a two stroke engine is less than that of a four stroke engine and the initial cost of installation of a two stroke propulsion plant is also much higher than running and maintenance cost of a 4 stroke engine. In 2 stroke engine, the amount saved on high grade fuel can compensate all other disadvantages and also reduce the whole operating cost of a ship.

Text 12 Starting Procedure for Turbine Generator on Ship

Like every other machinery, the turbine generator of the ship also needs to start under sequential starting procedure to avoid trouble free operation of the whole system. The correct procedure ensures that no part of the machinery goes through any kind of stress- thermal or mechanical. It also helps the ship to operate without wasting any extra time.

The correct starting procedure for steam Turbine Generator onboard ship is as follows:

1. Check turbo generator lube oil sump level and drain it for water. Replenish it if level is less than normal.

2. Start the lube oil priming pump from the local station and check the lube oil pressure. Put the priming pump on auto.

3. Check and fill up the Turbine Generator vacuum pump operating water tank to normal level.

4. Check vacuum condenser condensate level from the condensate pump. Put the pump on auto so that the level is maintained all the time.

5. Operate the steam drain valve to drain any condensed water from the steam line to avoid excessive hammering and vibration while starting turbo generator.

6. Open the main steam inlet valve for turbo generator.

7. Adjust the gland steam pressure to normal level.

8. Check and open the sea water valves for vacuum pump cooler, T/G lube oil cooler and vacuum condenser are opened.

9. Start the vacuum pump and bring up the vacuum in the condenser.

10. Open condensate pump valves and switch on the pump.

11. Check whether the condensate vacuum, gland steam pressure, steam inlet pressure, and lube oil pressure are normal.

12. Start turbo generator from the local station and close the drain in the steam line.

13. Check first and second stage steam pressure.

14. Check condenser vacuum and water level.

15. Check lube oil pressure and vibration levels.

16. Check turbo generator speed, voltage, frequency, vacuum, condenser level and other parameters.

17. Give control to remote station from the local control and take the TG on load.

TEXTS TO UNIT IV