What is a Lambda Control System in Marine?

What is a Lambda Control System in Marine?

With new, stringent pollution control regulations in place, manufacturers must design marine engines that meet these standards and do not compromise normal operation. To achieve this, engines incorporate various automated systems that not only reduce pollution levels but also improve efficiency and reduce other operating costs.

A Lambda Control System is one such system that controls the fuel injection system of a marine engine in response to load changes.

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Purpose of Lambda Control Unit

The primary function of any engine is to provide enough power to support the load placed on it. Loads may increase or decrease during operation, and for this purpose, excess fuel may be added to maintain performance.

A Lambda Control Unitis used to control the injection of excess fuel into the combustion chamber of a marine engine when the engine load changes (i.e., when the load temporarily increases).

This is achieved by controlling the two main components responsible for combustion: fuel and air. The controller monitors the relationship between charge air pressure and the engine fuel ratio at this load.

Working principle

The working principle of the Lambda controller is shown in the following figure:

When the engine load increases suddenly and momentarily, the Lambda controller regulates the fuel flow through the injection pump via the adjustment rod. To do this, it activates (1), which in turn commands the switch (2) to contact the piston rod (3) and push it downwards, thus closing the circuit.

As a result, the solenoid valve (4) opens, triggering the injection system to accelerate the turbocharger and increase the charge air pressure. This pushes the piston (3) back into the Lambda cylinder (5). When the Lambda value or ratio is reached, the solenoid valve closes, deactivating the injection system.

If the system is left running for more than 10 seconds, the solenoid valve activates, triggering a system fault alarm.

Fuel consumption limitation during start-up

During start-up, the Lambda controller acts as a fuel consumption limiter.

This prevents excessive smoke and too fast throttle response during start-up.

Advantages

• Reduces excessive visible smoke emissions when the engine load increases suddenly.
• Improves overall engine efficiency.
• Reduces carbon deposits in the engine exhaust system (exhaust valves, exhaust pipes, exhaust inlets, etc.).
• Reduces maintenance costs by reducing dirt accumulation on parts.

What does lambda measure?

Lambda is the ratio between the air actually in the cylinder and the air needed to burn the injected fuel completely. At a ratio of one the two match exactly. A diesel runs well above that, with surplus air, because fuel and air only mix during injection and the surplus is what gets the last of the fuel burnt.

Push the ratio down by adding fuel faster than air arrives and combustion goes incomplete. The visible result is black smoke. The lasting results are soot through the exhaust system, higher exhaust temperatures and deposits on valve seats and turbocharger nozzle rings.

Air is the side that cannot answer quickly. The turbocharger is driven by exhaust gas, so charge air pressure only rises after fuelling has already increased. The lag between the two is the window the controller exists to police, and it is why the limit is set against charge air pressure rather than against engine speed.

What a failed limiter looks like from the control room

Two opposite symptoms point at the same system. An engine that will not take load, with the governor demanding more while the rack stays held back, suggests the controller is limiting against a charge air pressure signal it is not receiving. A failed transmitter or a blocked sensing line does this with nothing wrong in the engine at all.

The other symptom is heavy black smoke on every load increase, which says the limiting function is doing nothing. That is a housekeeping problem before it is an emissions one, because the soot it lays down in the exhaust gas economiser is what an uptake fire starts in.

Settings are not free to move. The engine carries an approved technical file for its nitrogen oxide emissions under MARPOL Annex VI, and the components and settings that affect injection are listed in it. An adjustment made to cure smoke can put the engine outside that file, and it surfaces at survey rather than in the running.