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Unit injector vs Common rail

Posted on 12/12/2016 10:25:16 AM

Depending on what area you operate in, there are different needs and requirements on the equipment. To achieve maximal output on marine vessels, it is important to use diesel engines specifically adapted to the operating conditions. Here the common rail parts specialist - China Balin Power Co.,Ltd will describe the two fuel injection systems Unit injector and Common rail, and the differences between the two.


Requirements on diesel engines in the marine vessel industry
There are a couple of main reasons why professionals working with marine vessels have tough requirements on their diesel engines. As climate change and pollution are becoming an increasing threat to our planet, it is more important than ever to comply with current emission legislation. A smart and fuel-efficient engine is therefore a must. Another aspect that the marine vessel industry is dependent on is the engine’s reliability. Unplanned downtime can be devastating for a business’s operations. To feel secure and safe during the engine’s whole life span is therefore crucial. Many diesel engines working in the marine vessel industry often perform at high speeds and power outputs, long periods at a time. For the engines to deliver excellent results and work at full capacity, they need to be robust, durable and maintain a high quality.

Fuel and air – two crucial factors a diesel engine need to function
Fuel and air are the two most basic and necessary things that a diesel engine needs to function, since oxygen molecules are required for the fuel’s combustion process. The combustion takes place when the piston compresses the air in the combustion chamber and the temperature rises to ignition temperature. When the fuel is injected, it ignites, causing the engine to run. Central to the diesel engine is the fuel injection system. It regulates the engine’s power and has a major impact on the efficiency and exhaust emissions.

A high pressure in the fuel injection system is beneficial for the environment
The unit used to measure the pressure in the fuel injection system is the metric unit bar. The higher the pressure in the fuel injection system, the more friendly it is to the environment. High pressure results in small fuel droplets with high energy which are needed for fuel and air to mix for clean combustion. For high power engines, a high quantity of fuel needs to be injected during a short period. To achieve this, a specific nozzle flow is selected. Normally, the main injection has to end at crank angles between 24 and 27 degrees, before the piston expose the cylinder wall. The surface of the inner wall is cold due to cooling water outside of the cylinder. That means the small amount of fuel that hits the wall will not be combusted and the lubricating oil will be diluted. If the lubricant disappears, the engine may soon be worn out. In addition, unburned fuel and soot will enter the engine oil leading to oil degradation. Long-term this will be costly for the vessel owners with the risk of engine failure and high service costs.

This is one of the reasons why one should never try to tamper with the power setting of the engine. To prevent this from happening in the future, all injections outside the area where the cylinder walls are exposed will be cut into a series of very small injections to avoid the individual injections to hit the cylinder wall.

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