MAN ME-GI(ME engine with Gas Injection)
The MAN ME-GI (ME engine with Gas Injection) dual-fuel electronic fuel injection main engine is a significant innovation in the field of marine power. It combines high-pressure gas direct injection technology with an intelligent electronic control system, significantly enhancing environmental performance and fuel flexibility. The following provides a detailed analysis from four aspects: working principle, core components, differences from traditional ME-C main engines, and future development trends.
一,MAN ME-GI
I. WORKING PRINCIPLE OF MAN ME-GI BINARY FUEL ENGINE
1. Diesel Cycle High-Pressure Direct Injection Technology
Fuel Injection: At the end of the compression stroke (near the top dead center), a small amount of diesel (accounting for 3-5% of the total fuel, approximately 8 g/(kW·h)) is injected as an ignition source, utilizing the diesel self-ignition property for compression ignition.
High-Pressure Gas Injection: After the ignition of the fuel injection, natural gas is directly injected into the cylinder at a high pressure of 300 bar, ignited by the ignition source to achieve efficient combustion.
Fuel Adaptability: Supports various gas fuels such as LNG and LPG, has no strict requirements for methane content, and has good anti-explosion performance.
Figure 1：Diesel and Otto cycles operate
2. Operating Modes
Gas mode: Operates when the load is between 25% and 100%, with the fuel supply rate remaining constant and natural gas serving as the main fuel.
Minimum fuel mode: Minimizes the fuel supply rate, and the gas supply rate adjusts according to the load.
Pure fuel mode: Automatically switches to this mode when the load is low (<25%) or when the gas system fails.
II. Detailed Function Descriptions of Each Core Component
1. New Gas System Components
Double-walled gas pipe:
The inner pipe conveys 250-300 bar high-pressure gas, while the outer pipe is filled with ventilation air or inert gas to form a barrier.
The ventilation system exchanges air at a rate of 30-45 times per hour. The HC sensor detects leaks (if the concentration exceeds 60% LEL, it automatically switches back to the fuel mode).
Figure 2: Structure Diagram of Double-Wall Pipe
Gas Injection Valve (GIV):
Hydraulic servo oil drive (with a pressure 25-50 bar higher than the gas), precisely controlling the timing of gas injection.
Figure 3: Gas Injection Valve
Gas Control Block:
Pressure accumulator: Stabilizes gas pressure, with a capacity 20 times that of a single cycle injection volume.
Window Valve: Controlled by the ELWI valve, opens only at specific crankshaft angles, limiting the maximum gas flow.
ELGI Valve: Controls the servo oil-driven gas injection valve to achieve precise injection timing.
Figure 4: Gas Block
Sealing oil system:
An independent electric pump supplies sealing oil at a pressure 20-25 bar higher than that of the gas, preventing gas from seeping into the hydraulic system. The small amount of consumed sealing oil is burned along with the gas.
Figure 5: Sealing Oil
Gas Valve Group (GVT): Filters the gas and achieves system isolation, with a small volume but capable of withstanding high pressure. Low-temperature high-pressure pump: Pressurizes LNG to 250-300 bar to maintain stable common rail pressure.
2. Upgrades to the fuel/ignition system
Ignition injection valve:
Continues to use the fuel injection valve from ME-C, serving as an ignition fuel injector in gas mode, with the injection holes optimized to a dual-size design (small holes in gas mode to reduce fuel consumption).
FIVA valve control:
Electro-hydraulic proportional valve precisely regulates the timing and amount of ignition fuel injection.
3. Safety and auxiliary systems
Nitrogen purge block:
Injects nitrogen into the pipeline after TRIP in gas mode to reduce the risk of explosion.
Figure 6: Cleaning Block
Low-pressure system oil booster pump:
Rises the system oil pressure from 2 bar to 6 bar, replenishes oil to displace air and ensure stable oil supply to the hydraulic control unit (HCU).
GI extended control system:
SPCU (gas control unit), SACU (auxiliary control unit) manage the injection logic;
SPSU (safety unit), SCSU (cylinder safety unit) monitor leaks and abnormal flow rates, triggering emergency switching.
Figure 7: Dual-fuel Control System
III. Comparative Analysis with Traditional ME-C Electronic Fuel Injection Controller
ME-GI has added/modified the following systems based on ME-C:
|
System Category |
ME-C Engine |
ME-GI Additional Components |
Functional Differences |
|
Fuel Supply |
Single fuel oil system |
Double-walled gas pipe, GVT valve group, cryogenic high-pressure pump |
Supports 300 bar high-pressure gas supply |
|
Injection System |
Single fuel injection valve |
Gas injection valve (GIV), gas control module |
Dual-fuel independent/synchronized injection |
|
Sealing & Safety |
No sealing oil required |
Sealing oil system, hydrogen purge block |
Prevents gas leakage into the hydraulic system |
|
Control System |
Basic ECS control |
GI extension system (SPCU/SACU/SPSU/SCSU) |
Gas mode safety monitoring & redundant control |
|
Auxiliary Systems |
Conventional lubricating oil pump |
Low-pressure system oil booster pump unit |
Ensures stable HCU oil pressure |
Key differences:
Injection logic: ME-C only controls fuel timing, while ME-GI needs to coordinate the timing of fuel injection and gas injection to ensure fuel first and then gas.
Safety redundancy: ME-GI is equipped with dual sensors and an independent safety unit (SPSU/SCSU), which monitors abnormal gas flow (such as a pressure drop in the accumulator exceeding 23 MPa triggering a shutdown) in real time.
IV. Development Trends and Advantages/Disadvantages Analysis
Trends
1. Technological Upgrade (Mark II):
Fuel consumption for fuel injection has been reduced to 1.5% (from the original 3-5%), and the low-load capacity has been extended to 5%.
The double-walled tube design has been simplified, and a single pipe inlet and outlet have been adopted, reducing costs and the difficulty of nitrogen purging.
2. Fuel Diversification:
Derived ME-LGIM (methanol fuel) and ME-LGIP (liquefied petroleum gas fuel), supporting the research and development of ammonia fuel.
3. Low-pressure Version Supplement:
Launched ME-GA Otto cycle low-pressure engine (16 bar), targeted at the LNG transportation ship market, reducing initial investment.
Comparison of advantages and disadvantages：
|
Advantages |
Disadvantages |
|
Environmental Benefits: SOx reduction ≈95%, CO₂ reduction ≈23%. |
System Complexity: 20+ additional components, higher maintenance difficulty. |
|
Economic Efficiency: 50% thermal efficiency (equivalent to diesel), 25% lower fuel costs. |
High Initial Investment: Significant cost for gas supply systems (e.g., 300 bar compression equipment). |
|
Fuel Flexibility: Compatible with LNG/LPG/diesel, no methane number requirement. |
Low-Load Limitation: Gas mode unavailable below 25% load. |
|
Safety Features: Double-walled pipes + sealing oil + multi-layer monitoring, negligible methane slip. |
Emission Shortcoming: NOx reduction only 12-15%, requires EGR/SCR to meet Tier III standards. |
Summary
The MAN ME-GI engine overcomes the problem of natural gas's anti-explosion property through high-pressure direct injection and Diesel cycle. It significantly reduces emissions while maintaining the thermal efficiency of a diesel engine. Its core advantages lie in fuel adaptability and environmental friendliness. However, the complexity of the system and cost remain challenges. In the future, through the Mark II upgrade (low fuel consumption, high redundancy) and fuel diversification (methanol/ammonia), the ME-GI will continue to lead the low-carbon transformation of ship power, especially suitable for ships that pursue long-term operational efficiency and compliance. Traditional ME-C engine users can pay attention to MAN's modification services (such as methanol dual-fuel upgrade) to balance technological iteration and investment return.