CORROSION OF METALLIC MATERIALS BY ETHANOL

Corrosion reduction techniques used in SI engines fuelled by Ethanol: A Review

A Study by:Dr. B. S. Suresh, Shruthi N. Kumar, Jayghosh S. Rao, Ritvik N. Pai, S. Kamini

IntroductionToday transportation is a major anthropological activity. Advances in IC Engines and fossil fuel technology have transformed the concept of transportation.The infamous Oil Shock of 1973 jolted organizations into a state of action towards finding alternative fuels.

IntroductionGlobal warming, ever increasing emissions and depletion of fuel are banes of technological developments.Alternatives: Solar and Battery Electric propulsion.But the IC Engine is deeply ingrained into the lives of masses to discard it so abruptly.Another approach is to use a better fuel to power the engine, namely Ethanol.

Problems with conventional fuelsDepleting resourcesIncomplete combustionHazardous EmissionsKnockingIncreasing prices

Why is Ethanol an alternative?Produced mainly from cropsCleaner combustion reduced CO2Complete combustionBetter thermal efficiencyLower knockingHigher octane no. higher compression ratiosLess expensiveOwing to these properties, Ethanol is used as an additive to gasoline in varying quantities E10 to E85.Problems Ethanol posesWe find that ethanol has major advantages over gasoline, but a few problems were encountered with Ethanol fuel:Cold start problemsIncrease in NOx and CO2 emissionToo high SFC due to lower heat of combustionCorrosion of Metallic and degradation of non metallic parts of the engine.So a stock gasoline engine cannot be used with ethanol fuel for a sustained period.

CorrosionCorrosion is an electrochemical process where metal is oxidised and gradually destroyed.

[Effect of Galvanic Corrosion]

[1. Galvanic Corrosion Mechanics][2.Pitting Corrosion][3. Corroded Aluminium Fuel Sump]CORROSION OF METALLIC MATERIALS BY ETHANOLCorrosion is an electrochemical process Alcohols unlike gasoline are strong solvents and hence highly corrosive to some metal partsThe Corrosion Mechanics vary in different environments

Corrosion Of Metallic Materials By EthanolCorrosion Mechanics:General Corrosion - ImpuritiesWet Corrosion Azeotropic formation, galvanic basic wet cellDry Corrosion Polarity of molecule

Ethanol is also a good conductor of electricity. It acts as a very good electrolytePromotes Galvanic corrosion between two metals

General corrosionDue to ionic impurities such as chloride ions and acetic acidTime and temperature are also factors to be consideredHigh temperature condition and the products of combustion such as acids, aldehydes etc. accelerate the process of corrosionThe contaminants affect the solution chemistry and corrosion potentialDry CorrosionDry Corrosion is due to polar nature of ethanol and gives water as its by product. Hence the presence of water becomes inherent

Wet CorrosionAzeotropic form of ethanol and water causes wet corrosionThe presence of water and air inside the engine cylinder along with few of the combustion products like aldehydes and acids provide the atmosphere to initiate wet corrosionIncrease in the water content increases the conductivity and consequently electrolytic corrosionGalvanic Corrosion The opportunities for galvanic corrosion are manyHigher Si content in Al-319Cast Iron linerPiston rings

Conductivity of EthanolWater content in EthanolDiscontinuous protective film and contaminant attack

Sustained CorrosionCorrosion Reduction TechniquesChemical AdditivesAdditive propertiesASTM D5798-11 Standard Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition EnginesSource : http://www.astm.org/Standards/D5798.htmContaminants are currently limited by ethanol standardResearchers have experience with the micro-contaminants, but extensive studies are required to quantify the consequences with the use of ethanol.

Change of material systemsAll Aluminium Engine block (GM Vega Block)Hyper Eutectic Al casting alloys Higher wear resistanceNi-SiC liner CoatingFlex- Fuel Engines (GM, Porche, BMW, etc.)

Corrosion preventionSurface TreatmentAl sub system : Anodising, Plasma Electrolytic Oxidation (PEO)Steel Sub system : Cadmium, tin, nickel plating over galvanised or terne platingConclusionsEthanol poses problems to the well established material systems that are being used in the present automobile engines, one of which is corrosion.Means of decreasing and eliminating the persistent problem of corrosion have been suggestedSince various measures have been currently implemented that address the sustainability of this technology, it is a feasible alternative Ethanol use in Brazil, Sweden, Benelux, France , Switzerland and USEnergy security and autonomy in fuel management. Augments the development of other sectors particularly the agricultural sector