bio gas in engines

7/27/2019 Bio Gas in Engines

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Bio-Gas As Alternative Fuel In IC Engines

INTRODUCTION

A. Relevance :-The economic of India depends to a largeextent on the wheels of transport. Thespecter of economy ruin due to depleted oilreserves has changed the interest ofscientist and research work towardsalternative fuels for motor vehicle. Viablesubstitute for motor spirit are gaseoushydrocarbons, hydrogen gas, alcohol &electricity that run on hydrocarbon gas &electricity are still in the experimental stage.While alcohol is used as a fuel chiefly inBrazil, it?s feasibility as motor fuel dependson the successful cultivation & processing ofsugarcane. Gaseous hydrocarbons seem tobe the best immediate option presentlyavailable. These are mainly COMPRESSEDNATURAL GAS (CNG) & LIQUIFIED

PETROLIUM GAS (LPG). LPG is beingimported whereas CNG is available inabundance in India. Till recently, technologyto permit conversion of vehicles from petrolburners to gas burners had to imported, butnow due to the pioneering efforts ofdepartments of mechanical engineering atthe INDIAN INSTITUTE OFTECHNOLOGY, MUMBAI.India is largest cattle breeding country, thereis abundance of raw material for producingbiogas. Also municipal sewage can be usedfor this purpose.

The use of methane separated from biogasas a fuel will substantially reduce harmful


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engine emission and will help to keep theenvironment clean. Biogas consists ofapproximately 55-60 % of methane. It iseconomical and slurry can be used as

organic manure.One of the alternate technologies Sulabhpropagates is the biogas plant that utiliseshuman excreta as its raw input. In the last20 years, it has setup a hundred such plantsthroughout India. The plants? twin outputs,similar to those of cattle biogas plants, arenutrient-rich sludge and methane-richbiogas. The sludge is used primarily asmanure, and the biogas either as cooking

fuel or as street-lighting gas.

B. The Technology :-Biogas dates as far back as the 16thcentury, when it was used for heating bath-water in Persia. It has been used in India foralmost a hundred years (Sampat, 1995).The Indian government introduced large-scale biogas production in 1981 through theNational Project on Biogas Development.Biogas is produced by extracting chemicalenergy from organic materials in a sealedcontainer called a digester. 2 million biogasplants were in operation in 1995, and about10 million rural Indians were benefiting fromthe electric power and cooking

fuel the gas provided, and also from the richagricultural fertilizer the plant produces as abyproduct.Central to the generation of biogas is theconcept of anaerobic digestion, also calledbiological gasification. It is a naturallyoccurring, microbial process that converts


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organic matter to methane and carbondioxide. The chemical reaction takes placein the presence of methanogenic bacteriawith water an essential medium. The

anaerobic digestion process, as the namestates, is one that functions withoutmolecular oxygen. Ideally, in a biogas plantthere should be no oxygen within thedigester. However, efforts to completelyremove it will be prohibitively expensive.Oxygen therefore exists in the digester,dissolved mainly in water. Fortuitously,some microbes within the digester arefacultative anaerobes, i.e. they utilize

oxygen and lower the dissolved oxygenconcentration to levels suitable for otheranaerobic microbes to perform theirchemical reactions. Oxygen removal fromthe digester is important for two mainreasons. First, the presence of oxygen leadsto the creation of water, not methane.Second, oxygen is a contaminant in biogasand also a potential safety hazard. Due to

presence of oxygen, calorific value of biogasbecomes low.First, cow dung, the primary raw input foralmost all operating biogas plants iswidespread and easily available. India hasmore cattle than any other country (450million head, 19% of the world population).

Second, the cow is held in religiousveneration and its products are considered

purifying agents. Hence, there is a universalacceptance of even its dung, whichotherwise would instinctively be thought ofas repulsive. Dung (or gobar in Hindi) iswidely used in India for house construction(as an infill material and external plaster), inreligious rituals, as composted fertilizer and


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as a cooking fuel (dung cakes). Dungaccounts for over 21 percent of total ruralenergy use in India, and as much as 40percent in certain states of the country.

Third, only 27% of rural India has access toelectricity supplied by the national grid(ostensibly, 84% of all villages areconnected). Localized biogas plants obviatethe dependency on the grid by producingenergy from a locally controlled and easilyaccessible raw material.

C. Present Theory and Practices

i. Biogas cars: -Koges, Switzerland is developing a new fuelbased on biogas which would be ecofriendly and cheaper than petrol. Wastagefrom kitchens and gardens are collected,non-biodegradable matter removed andagain put into fermentation reactor. Here, inthe anaerobic environment microorganismstransforms the garbage into compost andbiogas called

kompogas. Gas obtained from 100kg. Ofwaste can fuel a medium sized car up to100km. The engine runs more quietly onkompogas, vibrates less and the exhaust isalmost odourless. At the present 150vehicles are running on kompogas.ii. In India, some projects are undertaken in

which diesel and biogas as dual fuel fordiesel pump.iii. In Israel, biogas is used as a fuel forloaded vehicles.

D. NeedTill date, LPG, CNG has been used as fuel.


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But they have their own limitations. LPG isexplosive, CNG is expensive. Methaneseparated from biogas is equivalent to CNGbut economical than CNG. Now-a-days the

whole world is facing energy crisis.Available sources of liquid fuel will bedepleted after few years. In this situationbiogas can serve as best alternative fuel.

E. Applications :-1. Fuels for internal combustion engine.2. Pump.3. Electricity generation.4. Domestic fuel for burners in kitchen.

PRESENT FUELS FORINTERNALCOMBUSTION ENGINE:-1. Gasoline.

2. Diesel.3. Alcohol4. LPG.5. CNG.6. Electricity.7. Solar.8. Producer gas.9. Hydrogen.

Present Fuels andLimitations:-There are so many fuels used in I.C.Engines, but they have certain physical andchemical properties. In other words, fuels


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used in I.C. Engine re designed tom satisfyperformance requirements of enginesystem, in which they are used. Thelimitations of fuels that are used presently

are as follows1. Gasoline contains many impurities. It haslow octane number. All petroleum fuelsoxidize slowly in presence of air. Theoxidation of unsaturated hydrocarbonsresult in formation of resinous materialscalled

gum and reduces its lubricating quality andtends to form sludge and warmish on piston

and rings. It has less knock resistance aswell as energy per unit mass. It has lessefficiency compared to other fuels. It hashigh cost.2. In alcohol, higher latent heat ofvaporization reduced charge temperaturesbefore combustion. Alcohols sufferdisadvantages of water absorption,corrosive and lubricant incompatibility.

3. In LPG, it reduces volumetric efficiencydue to its high heat of vaporization. Theroad sensitivity is very high. It is verycorrosive. Response to blending is verypoor. It has higher cost of transportation. Ithas higher cost for conversion kit,installation of extensive.4. In electricity, they use in initiallygenerated power stations that use fossil fuelof nuclear power. There are other problems

too. The problem is with batteries in thesevehicles. These batteries are quite heavyand life of these is also low. Cost ofreplacing these batteries is high.


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PREPARATIONOF BIO-GASI. Micro Organisms And Mechanism Of Bio-Gas Productiona. Micro Organisms-

An organic waste consist of many

organisms but the organisms useful forbiogas production arei. Aerobicii. Anaerobic

b. Constituents of Organic Waste ?The organic waste contains manyconstituents such as cellulose,Hemicelluloses, lignin, proteins, and starch,

water-soluble, fatsSoluble etc.c. Mechanism of biogas production: -Stage 1 It involves the decomposition ofcellulose, hemicellulos Lignin, starch,protein, fats etc. Into simpler organiccompounds like acids, alcohols and gaseslike CO2, H2, and NH3, H2S etc. by aerobicand anaerobic Micro-organisms.Stage 2: - The anaerobic organism or

methane bacteria utilizesSimple carbon compounds available fromfirst stage and produce methane.This is biogas production.

II. Bio-gas plants: -


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There are two types of plants-i. Daily fed or continuous type.ii. Batch fed or periodic type.

1). Daily fed or continuous type biogasplants: -It consists of 5 m. deep underground tank ofmasonry construction. It is known asdigester or fermentation well. The inlet tankis connected to digester by an inlet pipe andthe outlettank is connected to digester by the outletpipe as shown in figure. The gas holdercollects biogas produced in digester. It can

be taken for use through gas outlet pipe.The organic waste such as cattle dung ismixed with water in 1: 1Proportion and poured in inlet tankeveryday. This material is usually known assubstrate. Substrate gets collected in thefermentation well through the inlet pipe. Thetrapped air is removed from the digesterthrough the gas outlet and the gas holder is

placed in the position.When the plant is commissioned, aninoculation of the bacteria is brought fromexisting biogas plant and is injected in thedigester to accelerate the purpose ofdecomposition to produce biogas at fasterrate.Size of plant depends upon1. The required amount of gas daily and2 Available quantity of cattle dung daily.

After the digester is full of substrate within aweek?s time, the digester start coming outthrough the gas outlet pipe. It is displacedout. This gas can not burn. Initially high CO2contained in the gas makes it unsuitable foruse.Within 4-8 weeks, the microorganism


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develops sufficiently and biogas isgenerated. This stabilized gas burnscontinuously in the burner. The gas outlet iscovered with wire mesh to prevent a flame

rushing into the digester.The plant should be exposed to the sunlightand shielded from the wind to accelerate thegrowth of bacteria. The substrate should notbe added till the steady flame of gas isobtained at the burner. The plant isoperated at low pressure for proper burningof gas and proper fermentation.The used out substrate passing to outlettank through the outlet pipe. The residual

slurry gets stored in this tank. The solidresidue can be used for diluting the dung.Sometimes mixture is used in the digester tohelp digestion. The digester may besurrounded by water and heating coil tomaintain temperature.

Advantages: -1. Continuous gas output.2. Minimum space requirement3. Suitable for individual familyDisadvantages: -1. Substrate of uniform quality is desirable2. Daily attention is required3. Daily feeding is necessary

III. Purification of Biogas:-

Biogas coming from tank contains ?


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Composition:?Methane(CH4) 50-68%Carbon monoxide (CO2) 25-35%Hydrogen(H2) 1-5%Nitrogen (N2) 2-7%Oxygen (O2) 0-.1%Hydrogen Sulphide (H2S) Rare

Out of these CO2 does not help incombustion process but reduce the calorific

value of biogas. H2S is in minor quantity butit has corrosive action on combustionchamber and also reduces calorific value ofbiogas. Also traces of moisture are to beremove for better thermal efficiency. Soharmful gradients are removed and use onlymethane as a fuel.

Different Purification Processes:-1) Removal of H2S -

The gas coming out of system is heated to1500 Cand over ZnO bed, maintained at 1800 Cleaving process gas free of H2S.ZnO + H2S = ZnS + H2O.ZnSO4 + 2NaOH = Zn (OH) 2 + Na2SO42) Removal of CO2 ?CO2 is high corrosive when wet and it hasno combustion value so its removal is must

to improve the biogas quality.The processes to remove CO2 are asfollows ?a) Caustic solution, NAOH ? 40%NAOH + CO2 = NAHCO3

b) Renfield process ? K2CO3 - 30 %


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K2CO3 + CO2 = 2KCO3

3) Removal of NH3:-The chemical reaction is as:

NH3 + HCL =NH4Cl

4) Removal of H2O:-For the removal of moisture, we passed thegas from above reaction, through thecrystals of white silica gel.

PROPERTIES OF BIO-GASIn its pure state, it is color less, odorless,

tasteless. For safety reason, an odorant isadded so that any leak can be easilydetected because of typical smell.The composition of bio gas is neverconstant. Methane is by far the largestcomponent, its presence accounting forabout 95% of the total volume. Methane is asimple hydrocarbon, a substance consistingof carbon & hydrogen. There are many of

these compounds each has its own carbon& hydrogen atoms joined together to for aparticular hydrocarbon gas as fuel gas.Methane is very light fuel gas. If we increasethe number of hydrogen & carbon atoms,we have got progressively heavier gases,releasing more heat, therefore more energy,when ignited.Specific gravity of methane is .55 which isless than petrol & LPG. This means that

biogas will rise if escaping, thus dissipatingfrom the site of a leak. This importantcharacteristic makes biogas safer than otherfuels. It does not contain any toxiccomponent; therefore there is no healthhazard in handling of fuel.The air to biogas (stoichiometric) ratio by


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volume for complete combustion is 9.5:1 to10:1.Biogas has a very slow flame velocity, only.290 m/s. at its highest. The range of

flammability is 4 to 14% which can givegood combustion efficiency.Biogas has very high octane numberapproximately 130. By comparison, gasolineis 90 to 94 & alcohol 105 at best. Thismeans that a higher compression ratioengine can be used with biogas than petrol.Hence, cylinder head of the engine is facedso that clearance volume will be reduced &compression ratio can sufficiently increase.

Thus volumetric efficiency & power outputare increased. Because of its high octanevalue the detonation occur however high thecompression may be. The Boiling point ofbiogas is above 300 degree Celsius whilethe calorific value is 35.390 MJ/m3One of the promising renewable energysources is biogas, which is compound gasconsisting mainly of methane (CH4) and

carbon dioxide (CO2). It is normally formedwith the decomposition of organicsubstances. Because of its low energydensity, the gas is generally stored in high-pressure gas bomb. To store it in acondition of high density, it is also attemptedto store methane in the form of clathrate.The clathration of methane requiresnormally high pressure and lowtemperature. If the clathration of biogas and

methane could be achieved under thenormal pressure and temperature, thiswould make the gases a very useful energysource. In this study, the clathration ofmethane under the normal pressure andtemperature was first attempted by usingTetrahydrofuran (THF) as additive. Further,


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to realize the higher storage density ofmethane, CO2 must be removedbeforehand because not only methane butalso CO2 form clathrate. To achieve CO2

removal, the possibility of absorptionmethod using Monoethanolamine (MEA) isexperimentally investigated, aiming efficientbiogas utilization in final.

Advantages of Biogas : -1) It is light fuel gas.2) It mixes easily with the air.3) It is highly knocked resistant.4) Due to uniform distribution thermal

efficiency is higher.5) Biogas has a high octane number.6) It reduces pollution.7) Higher compression ratio can be usedwith biogas.8) Plants capital cost is low.9) Domestic fuels for burners used inkitchen.10) No toxic to skin.

REPORTHIGHLIGHTSPOTENTIALBENEFITS OFBIOGAS

A study released at the NGV Conference


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highlights the benefits of using biogas as asource of fuel for NGVs. Biogas consistsprimarily of methane and is given off inplaces where decaying organic material is

found. According to the report, one of theprimary benefits of capturing biogasgenerated at landfill sites, sewage wastetreatment plants, and animal feedlots wouldbe a substantial reduction in greenhousegas emissions. The report also finds thatcapturing and burning biogas would providesignificant reductions in toxic emissions andozone forming pollutants, and lowerparticulate emissions in the case of heavy-

duty vehicles. In addition, the report findsthat water quality could be improved as aresult of reduced waste runoff near siteswhere biogas is captured and used inNGVs.The potential reductions of greenhouse gasemissions presented in this paper arestaggering. Much of this benefit is derivedfrom capturing and burning methane

emissions that currently are released intothe atmosphere. The report indicates that anNGV using fuel derived from biogas thatotherwise would have been vented providesas much benefit as removing six petroleum-fueled vehicles from the nation's highways.Stated differently, use of biogas in NGVswould produce 600 percent less greenhousegas emissions when compared with usingpetroleum as a motor fuel.

Using biogas that currently is flared insteadof vented would provide about a 100percent net reduction in greenhouse gasemissions when compared with burningpetroleum motor fuel in a similar vehicle.The study also finds that utilization ofavailable supplies of biogas could potentially


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reduce the motor vehicle-relatedgreenhouse gas emission by more than 340million tons -- a 23 percent reduction inoverall emissions of motor vehicle

greenhouse gas emissions.The amount of natural gas that potentiallycould be produced from decaying materialaround the country is substantial. The reportindicates that biogas could displace about 6billion gallons of motor fuel a year,accounting for nearly four percent of all thegasoline and diesel currently used by motorvehicles. The report indicates that some ofthis biogas can be produced at prices

competitive with conventional petroleumfuels. Much of the fuel, however, is noteconomic at today's fuel prices, but couldeasily be made economic if the right typesof incentives or credits were provided.

BIOGAS in

INTERNALCOMBUSTIONENGINE1. S. I. EnginesThe only adoption for a spark ignition engineis a gas (not gasoline!) carburetor to work atthe supply pressure (just like an LPGconversion, but an evaporator would not beneeded as the storage pressure is low). It isalso a good idea to scrub the H2S (as itcauses corrosion) and toderate the engine (unless you want toreplace it each year if operating


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continuously).Modification of S.I. Engine -S.I. engines can run completely on biogas,however, the engines are required to be

started on petrol at the beginning,conversion of S.I. engine for the entry ofbiogas, throttling of intake air & advancingthe ignition timing. Biogas can be admittedto S.I. engine through the intake manifold &air flow control valve can be provided on theair cleaner pipe connecting air cleaner &carburetor for throttling the intake air asshown in fig.2. C.I. Engine :- Diesel engines also need a

gas carburetor and scrubbing, but requireatleast 10% diesel via the injectors for ignition(and cooling). The initial starting of dieselengine is done on pure dieselModification of C.I. Engine:?C.I. engine can operate on dual fuel & thenecessary engine modification includeprovision for the entry of biogas with intake

air, provision of carburetor & system toreduce diesel supply, advanced injectiontiming. The entry of biogas and mixing ofgas with intake air can be achieved byproviding the mixing chamber below the aircleaner which facilitate through mixing ofbiogas with air before entering into thecylinder. The arrangement is shown in fig. islargely used in stationary enginecommercially available in India. The

capacity of mixing chamber may be keptequal to the engine displacement volume.The pilot injection of cycle is required to beadvanced for smooth and efficient runningof engine on dual fuel. The admittance ofbiogas into the engine at the initial stageincreases engine speed and therefore a


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suitable system reduces the diesel supplyby actuating the control rack needs to beincorporated.There is a wide range of thoughts on what

treatments should these biogases besubjected to before being used as fuel. Mostoperators simply remove the water presentin the biogas, leaving it to the enginemanufacturers to design engines which willcope with the impurities inevitably includedin the biogas (significant maintenancecosts); other Operators are seriouslyevaluating maintenance costs against initialinvestments in biogas clean up technologies

such as has been developed by AcrionTechnologies (although Acrion'stechnologies are mainly aimed at biogascontaminant removal and separation intomethane and carbon dioxide as feed stocksfor a variety of commercial applications).

PRACTICAL

DIFFICULTIESTo use the biogas as a fuel in SI enginethere are some practical difficulties. It is notpossible to compress the methane,separated from biogas by available method,because the gas could be liquefied throughchilling below -161 0C.This process is adapted by installing theunits required when there use of methane

separated from biogas as a fuel. Since gascan not be compressed it requires largespace for storage.

PERFORMANCE


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1. In purification method, by reducing CO2and moisture along H2S impurities inbiogas, the engine performance isimproved.

2. Effect of spark timing :-Biogas is slow burning fuel. Hence in orderto get optimum engine performance, sparktiming does not advance, and thencombustion continues in major part of theexpansion stroke. This reduces effectivework done. By advancing, spark timingpower is improved on low speed at partialthrottle condition as well as high speed atfull throttle condition.

EXHAUST EMMISSIONSThe exhaust emission contains threespecific substances which contribute the airpollution, hydrocarbon, carbon monoxide&oxides of nitrogen. Hydrocarbons are theunburned fuel vapour coming out with theexhaust due to incomplete combustion.Hydrocarbon also occurring in crankcase by

fuel evaporation. The emission ofhydrocarbon is closely related to manydesign &operating factors like inductionsystem, combustion chamber design, airfuel ratio, speed, load. Lean mixture lowerhydrocarbon emission.Carbon monoxide occurs only in engineexhaust. It is the product of incompletecombustion due to insufficient amount of airin airfuel mixture. Some amount of CO is

always present in the exhaust even at leanmixture. When the throttle is closed toreduce air supply at the time of starting thevehicle, maximum amount of CO isproduced.Oxides of nitrogen are the combination ofnitric oxide & nitrogen oxide &availability of


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oxygen are the two main reasons for theformation of oxides of nitrogen. The sparkadvance means lower peak combustiontemperature. It causes high NO

concentration in the exhaust. With biogas,co emission levels are low than that ofgasoline.

Comparison of Exhaust Emission :-

METHANE Vs GASOLINEPower Reduction 11%CO Reduction 99%HC Reduction 99%

NO Reduction 59%ISFC Increase 19%

Reference:http://www.seminarprojects.com/Thread-bio-gas-as-alternative-fuel-

in-ic-engines?pid=971#pid971#ixzz13YqTtbjq
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bio gas in engines

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