Lambda Control is a control system for the control of air-fuel ratio in engine. It is used to regulate the excess fuel injection in combustion chamber of marine engine when there is a change in load. Lambda controller performs by controlling the 2 elements which is quintessential for combustion i.e. fuel and air. This technology is commonly used by MAN Diesel for their engines like L23/30H MK 2 generator sets.
In a simple way, 4-stroke engine (auxiliary engine) doesn’t have auxiliary blowers like main engine. So, during starting period of auxiliary engine, to get proper rpm of turbocharger poor combustion takes place and generates smoke. To avoid this problem, there are 2 popular system i.e. Jet assist system & Lambda controller. This issue is more common in constant pressure turbocharger and that’s why many auxiliary engine designs have pulse turbocharger.
In Jet assist (Air assist) system, starting air is used to boost the charge air pressure when engine is started. Air is fed to the compressor side of turbocharger which increases the volume of air and thus charge air pressure increases. It provides good combustion and eliminates the formation of smoke.
Lambda controller senses the relation between the charge air pressure and fuel index of engine at particular load and increases the load response ability.
Air-fuel ratio (AFR) is very important for combustion process. IC Engine needs excess air for efficient combustion. It is the ratio of mass of air and mass of fuel.
Lambda is nothing but the ratio of actual air-fuel ratio and ideal air-fuel ratio. For Internal Combustion Engine (IC Engine), lambda must be greater than 1 i.e. actual air-fuel ratio must be greater than ideal air-fuel ratio.
Lambda Controller system consists of jet system solenoid valve, shut down solenoid valve, lambda cylinder, piston arm & piston, switch (pick-up switch), regulating arm, electrical circuit etc. It has connection for compressed air for supplying additional air to the system.
When load increases, governor increases the fuel index on the injection pumps and then regulator arm is turned. Pick-up switch touches the piston arm and pushes piston to close the electrical circuit.
As circuit completes, the solenoid valve of jet system opens. This valve is connected for delivering compressed air and when valve opens, it supplies compressed air to turbocharger. This additional air increase the charge air pressure. When lambda (Ratio of air-fuel ratio) becomes sufficient for combustion then it deactivates.
There is also a jet system failure alarm for the indication of jet system which is activated for more than 10 seconds.
- It reduces smoke emission due to sudden increase in load. It helps in generation of clean exhaust gas.
- There is significant improvement in load ability.
- There is less probability of fouling of exhaust system like exhaust valve, manifold etc.
- During starting, it limits the fuel index i.e. acts as a fuel index limiter.
- It helps to avoid the surging of turbocharger also.