Common Rail Fuel Injection in Marine Engines Explained 


A.k.a. Common Rail Direct Injection (CRDi) is a cutting-edge technology in marine engines. The innovative module is widely appreciated for zero-emission and part load optimisation possibilities. Common rail fuel injection is an electronically-controlled pressurised injection mechanism to prevent fuel wastage for smoke-free operation at the load.  

In this guide, we provide an overview of the common rail injection technology used in modern marine diesel engines. Read on to explore the best-in-class engines with common rail configurations from leading brands. 

What is a Common Rail Fuel Injection System 

The common rail injection system is a type of manifold with a fuel oil storage unit. This part lies below the cylinder cover along the length of a marine diesel engine. It acts as a framework, connecting all cylinders to a common rail unit for high-pressure air-fuel supply.  

The mechanism regulates uniform fuel pressure for all rpm/loads. Engines with integrated common rails ensure smokeless combustion and enhanced fuel economy to meet strict maritime emission regulations. 

Composition in Common Rail Injection System in Marine Engines

common rail fuel injection system is composed of several marine parts configured to meet the specific fuel supply requirements. 


The rail is a dense-walled tubing (to bear high pressure up to 300 MPa) serving as an accumulator/reservoir for the even distribution of fuel to all the injectors in the system. It regulates hydraulic capacitance to the high-pressure circuit to eliminate pressure dropping to a significant level

High-pressure Fuel Injection Pump

High-pressure pumps regulate the fuel pressure as per combustion requirements. This pump delivers pressurised fuel to the rail for high-precision injection. It features a storage tank for compressing the fuel. 

Injector Inlet Pipe

High amplitude oscillations occur in the injection system due to high-frequency waves generated by high amplitude and low pressure. The injector inlet pipes must have an accurate dimension to reduce the impact of pressure oscillations. 

Atomizer Nozzle

This attachment on the injector tip delivers fuel into the combustion chamber. 

Feed Pump 

The feed pump induces a suction to extract fuel from the storage tank. 

Fuel Filter

Removes the residues and particulates from the fuel to support high-quality, smokeless combustion. 

Engine Control Unit (ECU)

The ECU is an integral part of the internal combustion engine. This system can be integrated into modern marine engines for controlling the injection and combustion. It leverages data from various engine sensors, signal inputs, preset numeric tables, and digital equations to control the quantity and ratio of the air-fuel mixture, frequency of injection, rail pressure control, ignition timing, etc.   

Top 5 Marine Engines with Common Rail Injection Configuration 

There have been several innovations to boost the efficiency of the common rail mechanism for enhanced engine performance, fuel economy, and emission control. Following are the leading marine engine models featuring state-of-the-art fuel injection systems powered by common rail technology. 

#1. Wärtsilä Sulzer RT Flex Series             

Wärtsilä Sulzer 6RT-flex58T-B was the first low-speed diesel engine with a propulsion system powered by common rail injection. The engine created a benchmark during the initial sea trial in GYPSUM CENTENNIAL in 2001. 

#2. MTU Series 4000

The common rail injection scheme was pioneered by Vickers in 1916 for operating G-class submarines. However, MTU introduced the modern electronically-controlled common rail fuel injection in 1996 with its line of Series 4000 engines. 

#3. Caterpillar C8.7 Propulsion

The common rail system in this Cat marine engine offers superior low-end torque and fuel efficiency. With a proven zero-emission trial successfully, the engine has secured the EPA Tier 3 certification. 

#4. Yanmar JH-CR Series 

This engine featuring a custom-tailored common rail design offers extensive power solutions for multiple applications. It is ideal for small motorboats, sailboats, and commercial watercraft. 

#5. DI13 076M. 643 kW (875 hp)

This Scania engine applies the common rail configuration for extra high-pressure injection for superior torque and low exhaust emission at reduced fuel consumption. 

Looking to upgrade your watercraft to an efficient common rail fuel injection-powered engine?

Alfa Marine Spare Parts is your one-stop store for purchasing marine engines and OEM spare parts from renowned brands

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