Section 5 Compressors and Gas Engines

501. Gas compressors

1. The fuel gas compressor is to be fitted with accessories and instrumentation necessary for efficient and reliable function.

2. The gas compressor and fuel gas supply are to be arranged for manual remote emergency stop from the following locations:

(1) Cargo control room (relevant for cargo ships only);

(2) Navigation bridge;

(3) Engine control room; and

(4) Fire control station.

502. Gas engine design general

1. The last gas valve prior to the gas engine is to be controlled by the engine control system or by the engine gas demand. All gas engine components, gas engine systems and gas engine subsystems are to be designed to exclude any explosion at all possible situations or to allow explosions with- out detrimental effect and to discharge to a safe location. In this case, the explosion event is not to interrupt the safe operation of the engine unless other safety measures allow the shutdown of the affected engine.

(1) When gas is supplied in a mixture with air through a common manifold, sufficient flame arrest- ors are to be installed before each cylinder head. The mixture inlet system is to be designed to withstand explosions of mixture by means of:

(A) explosion relief venting to prevent excessive explosion pressures. It is to be ensured that

the explosion relief venting is installed in a way that it discharges to a safe location; or

(B) documentation demonstrating that the mixture inlet system has sufficient strength to contain the worst case explosion.

(2) The exhaust system is to be designed to withstand explosions of unburned mixture by means of:

(A) explosion relief venting to prevent excessive explosion pressures. It is to be ensured that the explosion relief venting is installed in a way that it discharges to a safe location; or

(B) documentation showing that the exhaust system has sufficient strength to contain the worst

case explosion.

(3) The crankcase of gas engines is to be provided with:

(A) crankcase explosion relief valves of a suitable type with sufficient relief area. The relief valves are to be installed in way of each crank throw and are to be arranged or provided with means to ensure that discharge from them is so directed as to minimize the possibility of injury to personnel; or

(B) documentation showing that the crankcase has sufficient strength to contain the worst case explosion.

(4)

It is to be ensured that the explosion of unburned mixture within the exhaust system or the crankcase or the explosion of mixture within the mixture inlet is allowed without detrimental

effect.

2. The design of piping on gas engines is to follow the requirements in "206. System configuration" and "207. Gas supply system in gas machinery spaces".

3. The combustion of the gas mixture is to be monitored by monitoring of the exhaust gas or com- bustion chamber temperature.

4. The exhaust pipes of gas-fuelled engines are not to be connected to the exhaust pipes of other en- gines or systems.

503. Requirements for dual fuel engines

1. Start and normal stop are to be on oil fuel only. Gas injection is not to be possible without a corresponding pilot oil injection. The amount of pilot fuel fed to each cylinder is to be sufficient to ensure a positive ignition of the gas mixture.

2. In case of shut-off of the gas fuel supply, the engines are to be capable of continuous operation by oil fuel only.

3. Changeover to and from gas fuel operation is only to be possible at a power level and under con-

ditions where it can be done with acceptable reliability as demonstrated through testing. On power reduction the changeover to oil fuel is to be automatic. The changeover process itself from and to gas operation is to be automatic. Manual interruption is to be possible in all cases.

4. On normal stop as well as emergency shutdown, gas fuel supply is to be shut off not later than simultaneously with the oil fuel. It is not to be possible to shut off the supply pilot fuel without first or simultaneously closing the gas supply to each cylinder or to the com- plete engine.

504. Requirements for gas-only engines

1. The starting sequence is to be such that fuel gas is not admitted to the cylinders until ignition is activated and the engine has reached an engine and application specific minimum rotational speed.

2. If ignition has not been detected by the engine monitoring system within an engine specific time after opening of the gas supply valve, the gas supply valve is to be automatically shut off and the starting sequence terminated. It is to be ensured by any mean that any unburned gas mixture is flushed away from the exhaust system.

3. On normal stop as well as emergency shutdown, gas fuel supply is to be shut off not later than simultaneously with the ignition. It is not to be possible to shut off the ignition without first or si- multaneously closing the gas supply to each cylinder or to the complete engine.

4. For constant speed engines, the shut down sequence is to be such that the engine gas supply valve closes at idle speed and that the ignition system is kept active until the engine is down to standstill.