3. General Description of the High Pressure Gas Injection System

The aim of this section is to provide the reader with an overall conceptual understanding of the high pressure gas injection system designed for MAN B&W two stroke engines

3.1 High pressure gas injection principle

The principle of the high pressure dual fuel system is to start the combustion on a pilot oil injection (MDO/HF) followed by a high pressure gas injection into the ignited pilot oil. In this high pressure gas diesel process the gas is combusted immediately as it is injected which has the advantages:

• No gas slip from combustion chamber to crankcase or exhaust receiver

• No accumulation of unburned gas

• No knocking

Figure: 1 Low pressure otto process versus high pressure diesel process gas injection

Info no. Sub category Ident. no.

3092815 - 7

Title

Dual Fuel Operation Page no.

6 (28)

Date Des. Chk. Appd. A. C. Change/replacement C. no.

2011-03-16 JAB JAB ER Document transferred to template. 0

3.2 Design criteria and concept of the gas system

The overall focus in the development of the dual fuel system concept has been personal safety. Secondly, it has been important to sustain engine reliability.

These two focus areas lead to the following general design decisions and concepts:

1. Gas safe engine room

All gas components inside engine room are encapsulated and the duct is vented by a suction fan. See ref.1

HC sensors at the air outlet detects gas leakages and if the gas concentration becomes too high a gas shut down is released (see Process FMEA)

2. A single failure result in gas shut down or gas stop

For safety reasons a detected single failure on a safety unit results in gas shut down while a detected single failure on a control unit results in gas stop.

3. The gas system must not affect the engine running on MDO/HFO

In case of gas shutdown the gas injection is stopped immediately and the engine continues almost bump less on fuel without load reduction.

In case of gas stop the gas injection is ramped down to minimum gas injection and then gas injection is stopped. Engine speed and load is maintained all the time during the changeover to fuel running.

4. The gas system is an add on to the ME engine

All gas components on the engine are dedicated for gas running and the gas control system GI-ECS is a standalone control system having a simple electrical interface to the ME-ECS.

5. Simple electrical interface to the ME-ECS

The interface between the ME-ECS system and the GI-ECS system is limited to very few electrical signals

• Governor index (from  ME)

• Injection timing (from  ME)