Effects Of Siloxane On Engines And Resulting Damages

THE EFFECTS OF SILOXANE ON ENGINES AND RESULTING DAMAGES

Silicon dioxide accumulated in the combustion chamber of the gas engine damages various parts of the engine such as pistons, cylinder heads, valves, and shortens the life of engine oil and oil filters. As a result of this, the maintenance frequency of the gas engine increases, knocks occur in the combustion chamber of the engine, electrical energy conversion losses occur and the consumption of spare parts increases. These effects can be listed in detail as follows:

  • Increased lubricating oil consumption due to silicon dioxide accumulating in pistons causing scratches on liners and failure of good sweeping of piston rings [1]
  • Inability to expand the piston rings and increased oil consumption in the combustion step as a result of silicon dioxide covering the piston rings [1]
  • Orthosilicic acid (H4SiO4), resulting from combustion of siloxane in the combustion chamber, mixed with the oil, increasing the acidity of the oil and causing the oil to change early [1].
  • Coating of the valves by silicon dioxide from siloxane combustion and valves can not fit into the seats and occurance of the valve torching (flame leakage out of the combustion chamber) and valve guttering [1]
  • Knocks caused by premature pressure zones in the combustion step due to silicon dioxide, which heterogeneously covers the combustion chamber, and the risk of knocking on the engine components and bearings in a short time [3]
  • Degradation of oil film as a result of scratches caused by silicon dioxide on cylinder surfaces and dry friction of piston rings on liner surfaces [1]
  • Scratching of the engine surfaces where the silicon dioxide particles in the lubricating oil come into contact with, including bearings [1]
  • The accumulation of silicon dioxide in the spark plugs (silica is used as an electrical insulation material in the industry and its electrical insulation is very high) affects the design ignition voltages, the spark plugs need to be cleaned more frequently and the need for early replacement [1]
  • Due to the silicon dioxide coating on the thermocouple and knock sensors and because of the the insulating effect of the silicon dioxide, the sensors show incorrect values and the engine’s fuel / air ratio is strayed from the optimal values, the engine efficiency decreases and the emissions increase, as well as the electronic systems that protect the engine from excessive temperature and knock damage due to heavy operation damage.

EFFICIENCY AND POWER LOSSES IN THE ENGINES RESULTING FROM SILOXANE

 

Silicon dioxide, which starts to accumulate with the combustion of siloxane in the combustion chamber of the engine, increases its effect from the moment it starts to accumulate and causes energy conversion losses in the following ways:

 

  • Power loss due to knocking caused by contamination (eg 1250 kW instead of 1415 kW) [1]
  • Loss of power due to loss of efficiency at low load operation (given in the technical documentation of the engine where the efficiency of the engine at 1415 kW drops to 39.3% from 40.5% at 1060 kW. (The efficiency loss at intermediate powers must be calculated by interpolation). [2]
  • Due to the contamination, changing of the designed compression ratio of the combustion chamber, engine burning excess gas for the same power relative to the clean engine, deterioration of emissions, inability to reach full load in the future [3]
  • Contamination of the combustion chamber resulting in changing of designed chamber geometry and heat transfer efficiency, causes the engine to burn excess gas for the same power relative to the clean engine, deterioration of emissions, failure to reach full load in the future [3]
  • Decrease in the volumetric efficiency of the engine due to debris around the intake valve, reduced valve opening and reduced intake air / fuel mixture flow of the engine (initial combustion of excess gas, deterioration of emissions, failure to full load later) [3]
  • Loss of combustion at low pressure and loss of combustion efficiency due to gas leakage of exhaust valve, which cannot be fully closed due to deposits around the exhaust valve (initial gas combustion, failure to full load later) [3]
  • Excess gas combustion and power loss as a result of the deterioration of the design geometry in the combustion chamber, which provides homogeneous combustion by turbulence of the fuel / air mixture due to the accumulated silicon dioxide layer, and the reduction of combustion efficiency [3]

 

As soon as the silicon dioxide accumulates in the ORC boilers, which transfer the heat energy of the exhaust gas to the thermal oil, it causes the following:

  • Forming an insulating layer on the finned pipes and the fins thus reducing heat transfer by 20% to 33%, resulting in the power loss [4].
  • Contraction of the gas cross-sectional area as a result of the formation of an insulating layer by holding onto the fin pipes and the fins, causing exhaust gas backpressure (causing the motors to run inefficiently or even stop after a certain backpressure value) [4]

 

Evaluation of the strategies that can be applied in situations where it is necessary to make power reduction in engines due to the harmful effects of siloxane in engines

 

  • To be content with the existing gas engines that can operate at low power:  As a result, it will not be possible to benefit from the maximum amount of gas that can be taken from the field.
  • Additional gas engine to activate: The additional gas engine can only be operated at full power and with high efficiency if several engines are running at low power. Otherwise, this additional engine will be able to run at low power and low efficiency. If the total missing power of the engine or engines running at low power due to the siloxane effects is less than half of the power of a normal engine (for example 1415/2 = 707 kW for a gas engine with 1415 kW power), the additional engine cannot be operated for a long time. As a solution, the power of normal running engines is slightly reduced and the remaining power to the additional engine to be started is increased to sufficient power for continuous operation of this engine. In this solution, the efficiency of normal engines will be reduced.

 

REFERENCES

  1. Florez-Alvarez J., Egusquiza E., Analysis of damage caused by siloxanes in stationary reciprocating internal combustion engines operating with landfill gas, Engineering Failure analysis, 35, 2015.
  2. Technical Description, Genset JGS 420 GS-L.L GE Jenbacher No Tolerance Datasheet, 5, 2008.
  3. Stępień Z., Intake Valve And Combustion Chamber Deposits Formation – The Engine And Fuel Related Factors That Impacts Their Growth, 240-241, 2014.
  4. Visser P., Gersen S., Van essen M., Regarding Specifications For Siloxanes In Biomethane For Domestic Equipment, 38, 2013.