Diesel Gas Engines
Introduction;- In this post on | diesel gas engines we will discuss about the Liquefied Natural Gas,Principles of Gas Engines and Engine Control Gas System. The post on diesel gas engines will provide the relevant information about the topics related to gas engines and generators used on board ships and Industries.
Advantages of Diesel Gas Engines
Marine and commercial power generation industry prefers the Gas engines for the following facts.
- To meet the compliance with the stringent emission regulation limits of SOX and NOX.
- Smoke pollution
Transportation Liquefied Natural Gas (LNG) is at -1630 to -1650 C at atmospheric pressure. This fuel has become popular as an energy source globally.
What is boil-off Gas?
Due to the imperfect insulation of the tanks, and the effect of heat causes the LNG to evaporate inside the tank producing the boil-off gas. Tank pressure increases due to the mixing of BOG with gas in the tank. To handle the pressure an alternative source is to release the pressure in to the LNG tank. BOG fuel is subject to reliquefaction and supplied to engines as fuel.
The LNG production is by following processes.
Natural Boil-off gas
In this process Boil-off gas is taken from the tank above the liquid gas. Natural boil-off gas contains Nitrogen and high methane contents and will have high resistance to knocking? The lower calorific value will be around 35MJ/nm3.
Forced Boil-off gas
In this process LNG is evaporated separately after extracting from the bottom of the tank. This gas will contain hydrocarbons in the liquid gas. The knocking properties will vary from case to case and engine to engine. This gas will have methane no. of 80 and LCV around 39 MJ/mn3. Forced boil-off gas is more popular as fuel than the Natural boil-of gas for the general shipping.
The most suitable gas as engine fuel is Natural boil-off gas since it has the better knocking stability due to the high methane contents contained in it. But the natural boil off gas is not available in plenty.
Hence the engine design preference is for the forced boil-off gas.
Principles of Diesel Gas Engines
Operating principles of the Gas Engines is of following two types.
- Otto gas Engines
- Spark Ignition Gas Engines
- Diesel Ignition Gas Engines.
Otto Cycle gas engines
Otto Cycle gas engines are with low NOX emissions with high efficiency. These engines meet the latest IMO compliance. These engines work differently with respect to efficiency at low load operations.
Diesel Cycle gas engines
On completion of the diesel pilot fuel ignition, high pressure gas injection in to the cylinders takes place. This type of design is compatible for the dual fuel operation also and can run satisfactorily 100 % on Diesel/HFO (Heavy Fuel Oil). High pressure gas at 300 bar is the requirement with the post exhaust treatment to comply with the emission regulations.
Advantages of spark ignition Gas engines.
- Use of low pressure gas supply at 4to 5 bar.
- Efficient at higher load.
- Low emissions and meats the regulations.
- Spark Gas Engines are Sensitive to ( Gas quality-Metahne No.)
High Pressure direct gas engine advantages
- Can operate on multi fuels ( HFO, MDO, LNG)
- Maintain Diesel Engine performance with high pressure gas injection at 300 to 350 bars.
- These engines are not sensitive to Gas quality.
- Simple evaporation with pumping of LNG to 350 bars.
- Fuel mixing flexibility.
Conversion to existing engine retrofitting is simple
Gas Engine Operation
Engine Control Gas System
Engine Control gas consists of following controls.
Speed & Power control:-
Engine control system adjusts the amount of gas injection by regulating the duration of gas admission valve for speed and power control.
Air Fuel Ratio Control
Opening of Waste-gate ratio will control the Air fuel ratio. The waste-gate controls the amount of bypassed exhaust gas to Turbocharger. The charge air pressure at each load point will decide the operation point.
Ignition system Control
Spark plug in the pre-combustion chamber is the ignition source of combustion. Engine control system controls tthe precise ignition timing and energy of ignition system
Gas Pressure and Valve control
Engine control system manages the control of gas pressure regulation, sequential gas valve operation and the operation of gas admission valve.
Cylinder Balancing and Knocking Control
In Gas engine control system is integrated with knock detection and monitoring of cylinder pressure. Engine control system transmits the pressure and knocking signals to the pane.
Engine Control system Overview
Introduction;- The Diesel Gas Engines power plants consists of following systems.
- Engine Control system
- Engine generator control panel
- Plant control and monitoring system
All the above systems are interfaced through Ethernet.
The engine control system consists of following panels and modules.
- Main Control panel
- Injection control module
- Spark ignition control module
- Cylinder monitoring Panel
- Local operating and Power supply panel.
Main Control panel
Main control panel is mounted on the Engine and consists of following controls.
- Main control of Gas
- Engine safety control
- Engine shutdown control
- Governor control
- Gas regulating unit control
- Cooling water valves control
- Air fuel ratio control Waste –gate
- Interface with LOSP (local operating & Power supply panel) and Engine generator control panel.
Injection Control Module
ICM (Injection control module) mounted on the engine and connected with the Gas admission valves and exhaust sensors temperature on each cylinder unit. Functions of the ICM are listed below.
- Drives the gas admission valve
- Measures the exhaust gas temperature
- Transmits the data to main control panel via CAN communication.
Cylinder monitoring panel
CMP monitors the combustion characteristics and intensity of knock at each cylinder & communicates the information with main control panel for monitoring and control for Diesel Gas Engines
CMP’s location is on Engine. CMP performs the following functions.
- Cylinder pressure signal measurement
- Process and measurement of knock signal
- Combustion characteristic calculation
- Calculation of knock characteristic
- Transmission of data to main control panel
Local Operating and Power supply panel
Operators use this panel mounted in self standing cabinet for the local operation and monitoring the engine.
LOSP performs the following functions on Diesel Gas Engines
- Local operation for starting, stopping and resting of alarms on engine.
- Display of Engine measurement and status.
- Display of alarms
- Display of events
- Test of actuators and valves in engine stop mode.
- Power distribution control to MCP, ICM, SIC ,CMP
Interface with main control panel
Engine Generator Control panel
Engine generator control panel for Diesel Gas Engines is installed in control room as self standing cabinet. Main functions of EGCP are as under.
- Remote operation for starting, stopping, and resting of alarms.
- Voltage control with the help of AVR.
- Opens and closes the generator circuit breakers.
- Emergency stopping of the engine. Safety control and protection of engine.
- Synchronization on auto and manual mode.
- Selection of power control mode.
- Setting of demand power.
- Engine and Generator measurement display.
- Display of electrical parameters.
- Displaying of alarm and events.
- Interface with plant control monitoring system
Monitoring and Plant control system for Diesel Gas Engines
PCMS is installed in control room. PCMS consists of Station PLC and operation station. PCMS controls and monitors the Engine and generator set.
Functions of PCMS are as under.
- Remote operation
- Auto or manual operation
- Emergency stop of engine
- Auto synchronisation
- Section of power control mode.
- Setting of power demand
- Engine and generator status display
- Display of electrical parameters
- Auxiliary equipment and switchgear display
- Tank level display
- Display of Alarms
The Best Book On Marine Diesel Engines
Pounder’s Marine Diesel Engines and Gas Turbines
Since its first appearance in 1950, Pounder’s Marine Diesel Engines has served seagoing engineers, students of the Certificates of Competency examinations and the marine engineering industry throughout the world.
Each new edition has noted the changes in engine design and the influence of new technology and economic needs on the marine diesel engine.
Now in its ninth edition, Pounder’s retains the directness of approach and attention to essential detail that characterized its predecessors. There are new chapters on monitoring control and HiMSEN engines as well as information on developments in electronic-controlled fuel injection. It is fully updated to cover new legislation including that on emissions and provides details on enhancing overall efficiency and cutting CO2 emissions.
After experience as a seagoing engineer with the British India Steam Navigation Company, Doug Woodyard held editorial positions with the Institution of Mechanical Engineers and the Institute of Marine Engineers.
He subsequently edited The Motor Ship journal for eight years before becoming a freelance editor specializing in shipping, shipbuilding and marine engineering. He is currently technical editor of Marine Propulsion and Auxiliary Machinery, a contributing editor to Speed at Sea, Shipping World and Shipbuilder and a technical press consultant to Rolls-Royce Commercial Marine.
* Helps engineers to understand the latest changes to marine diesel engineers
* Careful organisation of the new edition enables readers to access the information they require
* Brand new chapters focus on monitoring control systems and HiMSEN engines.
* Over 270 high quality, clearly labelled illustrations and figures to aid understanding and help engineers quickly identify what they need to know.
Conclusion;- I hope the post on Diesel Gas Engines has provided the usefu information to the reares.