An electronic control unit (ECU) is a device capable of making independent decisions, regarding the performance of an engine. It observes, regulates, and alter the key control units such as fuel, air, and injection timing. It achieves such high performance and low emission requirements; based on the signals from a series of sensors installed.
These sensors along with the electronic control unit constitute the electronic control module of an engine. Although they operate and adjust a different aspect of an engine, they achieve it mainly by adjusting fuel injection. Before electronic control units injection timings were adjusted and set mechanically.
The main advantage of using electronic control unit is that; it reduces the emissions and helps increase efficiency and engine safety. In a comparison an ECU engine consumes 15% less fuel and emits 22% fewer pollutants. Designed first in the 1970s for the heavy diesel engine installed on large ships; it’s now part of every new engine produced.
It throttles the fuel injecting based on the actual condition in the cylinder; whether its too rich or too lean mixture as compared to the optimum condition. Similarly in engines with variable valves timing the ECU also controls the airflow; thus affecting the engine performance. In a four-stroke engine, it also has to control and regulate igniting triggered by the spark.
The function of the Electronic Control Unit ( ECU )
Whether you drive a car or truck or work in noisy engine room like me running ship’s engine; they all run on variable speed based on traffic and operator requirement. Now in past carburetor ( four stroke engine ) and jerk pumps ( diesel engine ) used to manage; this process of creating proper air fuel mixture.
Yes they are cheap and versatile but have poor efficiency; leading to too reach or lean fuel mixture, loss of fuel and increased pollution. In four stroke engine they even reduce the volumetric efficacy of the engine and have trouble detonating. Furthermore they have more mechanical parts; meaning they needs more frequent maintenance.
The early electronic fuel injectors were just computer controlled carburetors or injectors with little to no sensors. But still even at such early stage they were sufficient to reduce emissions at the time. But as it become more and more advance with introduction of different sensors; it become an integral part of engine assembly.
This new method to inject just right amount of fuel into the cylinder using a solenoid operated injectors; that reduce the amount of fuel remain un-burnt or partially oxidised. More over since there is no effect of speed on atomization the engine performance at low speed is increased. Since variation of the mixture remains fixed it become easy to estimation true engine performance.
Electronic Fuel Injection System In Four Stroke Engine
Electronic fuel injection system can be implemented in four stroke gas engine by using single port and multi port injectors. One of the early commercially used system were the one with single point injectors. During the 80’s these single point injectors look similar to the carburetors; but with an injectors mounted throttle body of the engine with the circular air filter.
The complete system consists of ten key parts and sensors namely; oxygen sensor, engine temp sensor, idle speed control valve, manifold pressure sensor, crank position sensor, solenoid operated fuel injector, fuel pump module, ECU, ignition coli and power source ( battery ). This means there is much less injectors for an engine than number of cylinders.
On another hand modern four stroke engines use multi point injection system; in which there is single fuel injector for each cylinders. These injectors are then mounted on top of the engine as close to the intake valve; so as the spray make perfect air fuel mixture just before it gets into the combustion chamber.
In some cutting edge modern engine the fuel is injected directly into the cylinder. Since they too use separate injectors for each cylinder they also came under multi point injection system.
These high tech modern engines have electronic control unit that does not have a fixed value; meaning their performance can be further increased with a software update.
Electronic Fuel Injection System In Diesel Engines
Modern diesel engine use common rail injection system to comply with emission regulations and increase performance. The system consist of a common rail or distributor pipe; high pressure pumps, pressure regulating valves, injectors, electronic control unit and associated sensors to assist.
In diesel engines rather than adding fuel in the air intake manifold; it is simply injected directly into the cylinder. This helps in better performance and accuracy achieved by these; electronic fuel injection systems in diesel engine. Not just it allows for exact calculation of the fuel requirements; but also for higher compression ratio.
The fuel is transferred at a high pressure to the common rail; though a series of high pressure valve and pressure regulating valves. In small diesel engines the pressure maintained at the common rail is in between 40 to 250 bar. But in big engines such as in ship’s it amounts to 15,000 to 18,000 bar.
The electronic control unit or ECU take data from the various sensors about the oil pressure in the common rail; crank angle, engine speed, load, jacket water temperature, air temperature etc. Once analyzed based on the recommend settings feed into its memory it calculate the exact amount of fuel to be injected into the cylinder.
1 ) Brief History And Its Actual Operation
The modern smart engine as we called it are the fourth generation of electronically operated diesel engines. In the start there were these jerk’s pumps whole settings was decided based on computer generated value. Then after some years came the first engine where the exhaust valves were electrically controlled.
By mid 90’s it evolved from just electrically controlled exhaust valve to ECU controlled common rail injection system. Now the fourth and current generation is the one where; we not just use ECU but also alter its settings to increase performance. While the efficiency of an engine increase from one generation to another; so does there is a reduction in emissions.
Modern marine diesel engine are equipped with electrically controlled hydraulic control units; which take care of the injection and exhaust valve operating timings. In fact the complete electronically controlled system can be sub divided in three main parts; injection control, starting control and exhaust valve control.
Now the servo oil pump and other high pressure pumps send fuel oil to the common rail. Since the fuel actuator is connected with the rail; thus altering injection timing and duration. Now after sensing all the sensors the electronic control unit make the decision to actuate hydraulic injection control.
2 ) Altering Injection Timing in An Electronically Operated Engine
Since injection and exhaust valve operating timings are now controlled by hydraulic control units; actuated by the electronic control unit ( ECU ) of the system. This makes adjusting injection timing easier than before. While the ECU adjust these timing based on preset Ideal injection data and the data it get from the various sensors.
But it allows for manual adjustment from engine room manual control or the ECU controller installed in the engine control room. From engine control room it is rather too easy; just insert the authorization USB drive to validate your authority and make necessary changes to the rack settings ( + or – ).
Usually there are three types of USB access drives; one for the crew, another for developer and the shore authority or captain. Under normal condition settings are under auto; turn them from auto to manual and then simply adjust the injection timing or simply stop injection for an cylinder unit.
Using manual control panel in the engine room its a little tricky but yet simple. Just press the button “fuel control mode” then move across the setting using the rotating dial. Once you reach then based on the design either you have to wait for 2 seconds for auto select; or press the okay bottom to start advancing or retarding injection timing using the same dial.
Advantages Of Using Electronic Control Unit
- Improved volumetric efficiency
- High reliability and lower running cost
- Better atomization ( is independent of Crank speed – 4 Stroke )
- Lower SOx and NOx emissions
- Lower fuel consumption
- Injector position is not fixed meaning more flexibility in engine design – ( 4 stroke )
- Operational flexibility
- Reliable performance customization
- Increased life with lower idler speed.
- Made it easier to analyze and enhance engine performance.
How Does ECU Make Decisions – In Most Simplest Term
The ECU is much like a mini computer that make smart decision based on input data. An electronic control unit has various input device in the form of various sensors. Now when it get all the data it analyze and compare it with pre installed data fed into the system. After comparing the two it came up with solution that match the engine performance with the required value.
The system monitor the engine performance curve and made corrective adjustments to keep it within limits. In event it find anomaly it alert the operator and take steps as programed in the system. These programs are not permanent and thus can be modified to adjust how the system react to different conditions.
In much simpler terms consider the system memory as a table with different values; against expected final result. Now when the different values such as speed, throttle position, air and jacket water temperature is received. The system compare and analyze the data; it now know what is the expected engine performance and make corrective action.
Note: The article is produced on request from “John Kevin E. Quilaton“.
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