Technical field of the invention

The present invention relates to a method for operating an internal combustion engine, as defined in the preamble of claim 1. The invention also concerns an internal combus- tion engine arrangement according to the preamble of the other independent claim.

Background of the invention

Leakage of exhaust gas from the exhaust systems of internal combustion engines is a relatively common phenomenon, which causes different problems. For instance in en- gines with selective catalytic reduction, the emission limits might be exceeded, if part of the exhaust gas leaks out of the exhaust system before going through a catalytic converter. Another problem caused by leaking exhaust gas is corrosion problems due to impurities of the exhaust gases that enter the air intake system of the engine. Especially when fuels with high sulfur content, such as heavy fuel oil, are used, exhaust gases in the air intake system may cause severe corrosion problems. The leakage of exhaust gas is a particular problem in engines where fuel with high sulfur content is used together with water injection into the air intake duct. When sulfur dioxide (S0 ₂ ) in the exhaust gases reacts with water, it forms sulfurous acid (H ₂ SO ₃ ), which is further converted into highly corrosive sulfuric acid (H ₂ S0 ₄ ) or sulfate (S0 ₄ ^" ). If the exhaust gas leakage is not detected in time, severe damage can be caused to the engine.

Summary of the invention

An object of the present invention is to provide an improved method for operating an internal combustion engine. Another object of the invention is to provide an improved internal combustion engine arrangement. The method and the arrangement according to the present invention are characterized by the characterizing parts of the independent claims.

According to the present invention, in the method for operating an internal combustion engine that is located in an engine room, concentration of an exhaust gas component in the intake air is monitored. When the concentration of an exhaust gas component in the intake air is monitored, any leakage in the exhaust system of the engine can be detected quickly. Necessary actions for repairing the leakage or for otherwise limiting the damage caused to the engine or its auxiliaries can thus be taken in time.

According to an embodiment of the invention, the concentration of the exhaust gas component is measured from the air of the engine room. Gas sensors that are arranged to measure exhaust gas concentration in the engine room are easy to retrofit in existing systems and a variety of different sensors are suitable for the purpose.

According to an embodiment of the invention, the concentration of the exhaust gas component is measured from the intake system of the engine. It is possible to measure the concentration of the exhaust gases either from the intake system alone or both from the intake system and the engine room.

According to an embodiment of the invention the concentration of the exhaust gas component is compared to a predetermined limit value.

According to an embodiment of the invention, when the concentration of the exhaust gas component exceeds the predetermined limit value, an alarm is triggered. The alarm allows the operator of the engine to take the necessary actions for preventing damage to the engine.

According to an embodiment of the invention, when the concentration of the exhaust gas component exceeds the predetermined limit value, water injection into the intake duct or into the cylinders of the engine is terminated. Exhaust gases in the intake air are a problem in particular in engines with water injection into the intake duct or into the cylinders. When the water injection is stopped when an exhaust gas leakage is detected, the worst damage to the engine can be prevented.

According to an embodiment of the invention, the exhaust gas component of which concentration is monitored is S0 ₂ . Since S0 ₂ is the component of the exhaust gases that causes the worst problems, it is advantageous to measure the S0 ₂ concentration directly. According to the present invention, the internal combustion engine arrangement comprises an internal combustion engine that is located in an engine room and means for monitoring concentration of an exhaust gas component in the intake air.

According to an embodiment of the invention, the arrangement comprises means for measuring the concentration of the exhaust gas component in the air of the engine room.

According to an embodiment of the invention, the arrangement comprises means for measuring the concentration of the exhaust gas component in the intake system of the engine.

According to an embodiment of the invention, the arrangement comprises means for comparing the measured concentration of the exhaust gas component to a predetermined limit value.

According to an embodiment of the invention, the arrangement comprises means for triggering an alarm when the predetermined limit value for the concentration of the exhaust gas component is exceeded.

According to an embodiment of the invention, the arrangement comprises means for terminating water injection into the intake duct or into the cylinders of the engine when the predetermined limit value for the concentration of the exhaust gas component is exceeded.

According to an embodiment of the invention, the exhaust gas component of which concentration is measured is S0 ₂ .

Brief description of the drawings

Fig. 1 shows schematically an internal combustion engine arrangement according to an embodiment of the present invention. Detailed description of the invention

Embodiments of the invention are now described in more detail with reference to the accompanying drawing. In Fig. 1 is shown an internal combustion engine 1 that is located in an engine room 9. The engine 1 is a large internal combustion engine, such as a main or an auxiliary engine of a ship or an engine that is used for the production of electricity and/or heat at a power plant. The engine 1 is provided with a turbocharger 2. The turbocharger 2 comprises a turbine 2b that is rotated by the exhaust gases of the engine 1 and a compressor 2a for pressurizing intake air of the engine 1. A by-pass duct 5 that is provided with a by-pass valve 6 is arranged between the intake duct 13 and the exhaust duct 14 of the engine 1 for guiding excess intake air past the engine 1 when needed. Intake air for the engine 1 is taken from the engine room 9 and guided in the intake duct 13 to the cylinders 12 of the engine 1. The exhaust duct 14 guides the exhaust gases out of the engine room 9. The engine 1 is also provided with a waste-gate 7 and a waste-gate valve 8 for guiding part of the exhaust gases past the turbine 2b of the turbocharger 2 when needed.

For reducing the NOx emissions of the engine 1, the engine 1 is provided with means for introducing water into the cylinders 12 of the engine 1. When water is introduced into the cylinders 12, cylinder temperature during the combustion can be lowered and NOx emissions are effectively reduced. In the embodiment of Fig. 1, the means for introducing water into the cylinders 12 of the engine 1 comprise a humidifier 3 and a water tank 4. The humidifier 3 is located in the intake duct 13 downstream from the compressor 2a of the turbocharger 2. From the water tank 4, water is injected by means of a pump 15 into the humidifier 3, where the high temperature of the compressed air evaporates the water, which enters the cylinders 12 as steam. The humidifier 3 is provided with a water mist catcher that prevents water in liquid state from entering the cylinders 12. Instead of using a humidifier, the water could be injected directly into the cylinders 12 of the engine 1.

The engine room 9 is provided with a gas sensor 10 that is arranged to measure S0 ₂ concentration in the engine room 9. A second gas sensor 16 is arranged to measure S0 ₂ concentration in the intake duct 13 upstream from the compressor 2a of the turbocharger 2. The gas sensors 10, 16 are connected to a control unit 11, which controls the operation of the pump 15. The measured concentration of the S0 ₂ is compared to a predetermined limit value for the S0 ₂ concentration. By measuring the S0 ₂ concentration in the engine room 9 or in the intake duct 13, leakage in the exhaust system of the engine 1 can be detected quickly. When the S0 ₂ concentration exceeds the predetermined limit value, water injection into the cylinders 12 of the engine 1 is stopped until the leakage is repaired. The engine 1 can be kept running despite of the exhaust gas leakage. By terminating the water injection while the exhaust system is leaking, severe damage to the engine 1 can be avoided without having to stop the engine 1. Instead of or in addition to the termination of the water injection, it is possible that the control unit 11 is only arranged to trigger an alarm when an exhaust gas leakage is detected.

It is not necessary to have two gas sensors 10, 16, but a single sensor can be located either in the engine room 9 or in the exhaust system of the engine 1. Instead of measur- ing the S0 ₂ concentration in the intake air, the concentration of some other component of the exhaust gas, such as C0 ₂ , can be measured. If two gas sensors 10, 16 are used, it is also possible to arrange one of the gas sensors 10, 16 to measure the concentration of one exhaust gas component and the other sensor to measure the concentration of another exhaust gas component. Several engines 1 can be located in the same engine room 9, and exhaust leakages from all the engines 1 can be monitored with a single gas sensor 10, 16.

It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended independent claims. For instance, the gas sensor can be arranged to measure the concentration of the exhaust gas component from the suction chamber of the turbocharger or from the suction throat of air filter silencer.