ThermochemistryT Alrayyes

2

The mixture internal energy U and enthalpy H (units: kJ) is:

n

iii

n

iii hnHunU

11

where are molar specific values (units: kJ/kmol) ii hu and

n

iinn

1

The total number of moles in the mixture is:

Ideal Gas Model for Mixtures

The mole fraction, yi, of any given species is defined as:

n

ii

ii y

n

ny

1

1 and

n

iii

n

iii hyhuyu

11

The mixture molar specific internal energy and enthalpy (units kJ/ kmol) is:

3

Composition of Standard Dry Air

Air is a mixture of gases including oxygen (O2), nitrogen(N2), argon (Ar),carbon dioxide (CO2), water vapour (H20)….

For combustion dry air is taken to be composed of 21% O2 and 79% N2

by volume (yO2=0.21, yN2=0.79).

76.321.0

79.0

2

2

2

2

2

2 O

N

O

tot

tot

N

O

N

y

y

n

n

n

n

n

n

For every mole of O2 there are 3.76 moles of N2.

The amount of water in moist air at temperature T is specified by the specific humidity (w) or the relative humidity (F) defined as follows:

10 )(

22 FFTP

P

m

m

sat

OH

air

OHw

kg/kmol 84.28)28(79.0)32(21.0

22221

NNOOi

n

iiair MyMyMyMMolecular weight of air is

4

Combustion Stoichiometry

If sufficient oxygen is available, a hydrocarbon fuel can be completely

oxidized, the carbon is converted to carbon dioxide (CO2) and the hydrogen is converted to water (H2O).

Elements cannot be created or destroyed, so

C balance: 3 = b → b= 3H balance: 8 = 2c → c= 4

O balance: 2a = 2b + c → a= 5

OcHbCOaOHC 22283

# of moles species

The overall chemical equation for the complete combustion of one mole of propane (C3H8) with oxygen is:

OHCOOHC 22283 435

Thus the stoichiometric reaction is:

5

Combustion Stoichiometry

Air contains molecular nitrogen N2, if products are at a “low” temperature the nitrogen is not significantly affected by the reaction, it is considered inert.

222224

76.32

)76.3(4

NOHCONOHC

C balance: = b → b =

H balance: = 2c → c = /2

O balance: 2a = 2b + c → a = b + c/2 → a = + /4

N balance: 2(3.76)a = 2d → d = 3.76a/2 → d = 3.76( + /4)

Example: The stoichiometric reaction of octane (C8H18) = 8 and = 18

) 22222188 4798)76.3(5.12 NOHCONOHC

22222 )76.3( dNOcHbCONOaHC

The complete reaction of a general hydrocarbon CH with air is:

6

The air–fuel ratio (AF) represents the amount of air used per unit mass of fuel during a combustion process.

Air-fuel ratio (AF) is usually expressed on a mass basis and is

defined as the ratio of the mass of air to the mass of fuel for a

combustion process

m mass

N number of moles

M molar mass

Fuel–air ratio (FA): The reciprocal of air–fuel ratio.

9

THEORETICAL AND ACTUAL COMBUSTION PROCESSES

A combustion process is complete if all the combustible components of the fuel are burned to completion.

Complete combustion: If all the carbon in the fuel burns to CO2, all the hydrogen burns to H2O, and all the sulfur (if any) burns to SO2.

Incomplete combustion: If the combustion products contain any unburned fuel or components such as C, H2, CO, or OH.

Reasons for incomplete combustion: 1 Insufficient oxygen, 2 insufficient mixing in the combustion chamber during the limited time that the fuel and the oxygen are in contact, and 3 dissociation (at high temperatures).

Oxygen has a much greater tendency to combine with hydrogen than it does with carbon. Therefore, the hydrogen in the fuel normally burns to completion, forming H2O.

10

Fuel Lean Mixture

Fuel-air mixtures with more than stoichiometric air (excess air) can burn

With excess air you have fuel lean combustion

a fuel lean mixture has excess air, so g > 1

2222222

)76.3)(4

( eOdNOHCONOHC

g

At low combustion temperatures, the extra air appears in the products asO2 and N2:

Above reaction equation has two unknowns (d, e) and we have two atom balance equations (O, N) so can solve for the unknowns

11

Fuel-air mixtures with less than stoichiometric air (excess fuel) can burn.

With less than stoichiometric air you have fuel rich combustion, there is insufficient oxygen to oxidize all the C and H in the fuel to CO2 and H2O.

2222222

)76.3)(4

( fHeCOdNOHCONOHC

g

Fuel Rich Mixture

Above reaction equation has three unknowns (d, e, f) and we only have two atom balance equations (O, N) so cannot solve for the unknowns unless additional information about the products is given.

a fuel rich mixture has insufficient air → g < 1

Get incomplete combustion where carbon monoxide (CO) and molecular hydrogen (H2) also appear in the products.

12

The equivalence ratio, f, is commonly used to indicate if a mixture is stoichiometric, fuel lean, or fuel rich.

) )

) )s

mixture

mixture

s

AF

AF

FA

FA

/

/

/

/f

Off-Stoichiometric Mixtures

stoichiometric f = 1 fuel lean f < 1 fuel rich f > 1

Products)76.3(4

22

NOHC

Stoichiometric mixture:

Off-stoichiometric mixture:

Products)76.3(4

122

NOHC

f

fg

1

13

Off-stoichiometric Conditions

Example: Consider a reaction of octane with 10% excess air, what is f?

Stoichiometric : 22222188 4798)76.3(5.12 NOHCONOHC

10% excess air is:222222188 98)76.3)(5.12(1.1 bNaOOHCONOHC

O balance: 1.1(12.5)(2) = 16 + 9 + 2a → a = 1.25, N balance: 1.1(12.5)(3.76)(2) = 2b → b = 51.7

Other terminology used to describe how much air is used in combustion:

110% stoichiometric air = 110% theoretical air = 10% excess air

1.1 )76.3)(4

( 2283 g

g NOHC → mixture is fuel lean

) )

91.01/)76.4)(5.12(1.1

1/)76.4(5.12

/

/

mixture

s

FA

FAf 1.1

91.

11

f

18

First Law Analysis for Reacting System

Consider a constant pressure process in which nf moles of fuel react withna moles of air to produce np moles of product:

PnAnFn paf

Applying First Law with state 1 being the reactants at P1, T1 and state 2being products at P2, T2:

Reactants Products

ReactantsProducts

Reaction

State 1 State 2

Q

W

19

ENTHALPY OF FORMATION AND ENTHALPY OF COMBUSTION

The microscopic form of energy of asubstance consists of sensible, latent,chemical, and nuclear energies.

When the existing chemical bonds are destroyed and new ones are formed

during a combustion process, usually a large amount of sensible energy is

absorbed or released.

Disregarding any changes in kinetic and potential energies, the energy change of a system during a chemical reaction is due to a change in state and a change in chemical composition:

20

Enthalpy of reaction hR : The difference between the enthalpy of the products at a specified state and the enthalpy of the reactants at the same state for a complete reaction.

Enthalpy of combustion hC : It is the enthalpy of reaction for combustion processes. It represents the amount of heat released during a steady-flow combustion process when 1 kmol (or 1 kg) of fuel is burned completely at a specified temperature and pressure.

The enthalpy of formation hf : The amount of energy absorbed or released as the component is formed from its stable elements during a steady-flow process at a specified state.

21

To establish a starting point, we assign the enthalpy of formation of all stable elements (such as O2, N2, H2, and C) a value of zero at the standard reference state of 25°C and 1 atm.

22

Heat of Formation or Enthalpy formation

Enthalpy of formation : is defined as : the increase in enthalpywhen a compound is formed from its constituent elements in their natural form and ina standard state.Consider the following reactions taking place at atmospheric pressure andwith TP = TR = 298K

222

2222

/ 000,394 )()()(

/ 000,286 )()()(2/1

COkmolkJQgCOgOsC

OHkmolkJQlOHgHgO

Values for standard heat of formation for different species are tabulated

In these reactions H2O and CO2 are formed from their elements in theirnatural state at standard temperature and pressure (STP) 1 atm and 298K.

ofh

kmolkJQh

kmolkJQh

o

f, CO

o

Of, H

/ 000,394

/ 000,286

2

2

Reactions of this type are called formation reactions and the corresponding measured heat release Q is referred to as the standard heat of formation( ) so:

23

Heat of Formation for Different Fuels

24

Enthalpy of Reaction

Consider the case where the final temperature of the products is the same as the initial temperature of the reactants (e.g., calorimeter is used to measure Q).

ReactionQ

W

P1=P2=Po

T1=T2=To

The heat released under this situation is referred to as the enthalpy of reaction, DHR ,

fuel of kmolor kgper kJ :units )()(

)()(

D

Roii

Poii

RRii

Ppii

R

ThnThn

ThnThn

HQ

To

25

The maximum amount of energy is released from a fuel when reacted with astoichiometric amount of air and all the hydrogen and carbon contained in thefuel is converted to CO2 and H2O

Heat of Combustion

222224

76.32

)76.3(4

NOHCONOHC

DHR = HP – HR < 0 (exothermic)

DHR = HP – HR > 0 (endothermic)

This maximum energy is commonly referred to as the heat of combustion, orthe heating value, given per unit mass of fuel or air

26

Enthalpy Scale for a Reacting System

By international convention, the enthalpy of every element in its natural state(e.g., O2(g), N2(g), H2(g), C(s)) at STP has been set to zero

0)298,1( o

fhKatmhi.e,

Consider the following identity:

)]298,1(),([)298,1(),( KatmhTPhKatmhTPh

)]298,1(),([ ),( , KatmhTPhhTPh ii

o

ifi

sensible enthalpychemical enthalpy 298K T

K ip dTc298 ,

Therefore, the enthalpy of the i’th component in a mixture is:

27

28

FIRST-LAW ANALYSIS OF REACTING SYSTEMS

Steady-Flow Systems

When the changes in kinetic and potential energies are negligible, the steady-flow energy balance for a chemically reacting steady-flow system:

The enthalpy of a chemical component at a specified state

29

Taking heat transfer to the system and work done bythe system to be positive quantities, the energy balance relation is

Most steady-flow combustion processes do not involve any work interactions. Also, combustion chamber normally involves heat output but no heat input:

30

The higher heating value of a fuel is equal to the sum of the lower heating value of the fuel and the latent heat of vaporization of the H2O in the products.

Heating value: The amount of heat released when a fuel is burned completely in a steady-flow process and the products are returned to the state of the reactants. The heating value of a fuel is equal to the absolute value of the enthalpy of combustion of the fuel.

Higher heating value (HHV): When the H2O in the products is in the liquid form.

Lower heating value (LHV): When the H2O in the products is in the vapor form.

For the fuels with variable composition (i.e., coal, natural gas, fuel oil), the heating value may be determined by burning them directly in a bomb calorimeter.

31

Heat of Combustion

There are two possible values for the heat of combustion depending on whether the water in the products is taken to be saturated liquid or vapour.

Tp

T

S

hghf

From steam tables:hfg = hg – hf > 0

The term higher heat of combustion and heating value (HHV) is used when the water in the products is taken to be in the liquid state (hH20 = hf )

The term lower heat of combustion and heating value (LHV) is used when the water in the products is taken to be in the vapour state (hH20 = hg )

32

0

h(kJ/kg fuel)

T

Products with H2O (g)

Reactants

Products with H2O (l)

hfg,H2O per kg fuel

Dhlow

Dhhigh

Heat of Combustion, graphical

298K

33Source: Pulkrabek

Determine the enthalpy of combustion of methane (CH4) at 25°C and 1 atm, using the enthalpy of

formation data from the tables. Assume that the water in the products is in the liquid form.

40

Adiabatic Flame Temperature

Consider the following adiabatic constant pressure process:

For a given reaction where the ni’s are known for both the reactants and the products, Ta can be calculated explicitly.

Fuel

AirProducts

(Ta )

Reactants

(T1)

)()(

0)()(

1

Rii

Paii

RRii

Ppii

ThnThn

ThnThnQ

For a constant pressure process, the final products temperature, Ta, is known as the adiabatic flame temperature (AFT).

41

Adiabatic Flame Temperature

R

iiP

aii ThnThn )()( 1

P R

o

ifi

o

ifiR

T

ipiP

T

ipi hnhndTcndTcn ia

,,298 ,298 ,OR

) ) R

ii

o

ifiP

iai

o

ifi KhThhnKhThhn )298()()298()( 1,,

o

RHDSensible heat of reactants(equal to 0 if T1 = 298K)

Sensible heat of products

) )

P R

o

ifi

o

ifiR

iiiP

iaii hnhnKhThnKhThn ,,1 )298()()298()(

42

Ta,

Adiabatic Flame Temperaturewith products at equilibrium

43

Adiabatic Flame Temperaturewith products at equilibrium

nitromethane

octane

ethanol

hydrogen

Engine exhaust analysis• It is common practice to analyze the exhaust of an IC engine.• These sensors determine the chemical composition the hot exhaust by

various chemical, electronic, and thermal methods.• This information, along with information from other sensors, is used by the

engine management system (EMS) to regulate the operation of the engine by controlling the air-fuel ratio, ignition timing, inlet tuning, valve timing, etc

• Repair shops and highway check stations also routinely analyze automobile• exhaust to determine operating conditions and/or emissions. This is done

by taking a sample of the exhaust gases and running it through an external analyzer.

• Most of these analysis are based on dry analysis. by first removing all water vapor from the exhaust, usually by some thermo-chemical means.

The four-cylinder engine of a light truck owned by a utility company has been converted to run on propane fuel. A dry analysis of the engine exhaust gives the following volumetric percentages:

Fuel• Crude oil is made almost entirely from Hydrogen and Carbon (87%

carbon, 11 to 14% of Hydrogen by weight).

• Carbon and hydrogen can combine in many ways and form many different molecule compounds

• One set of crude oil might contain more than 25000 different compounds

• The oil compounds are separated by crack and/or distillation using thermal and catalytic methods at an oil refinery.

• Cracking is the process of breaking large molecular components into more useful components of smaller molecular weight

Distillation • Distillation is used to separate the mixtures into single components or

smaller ranges of components.

• Crude oil contains many thousands of different HCs, each has its own boiling point – lightest are gases at ambient T but can remain dissolved in heavier liquid HCs unless T is raised, heaviest are solids at ambient T but stay in solution unless T is lowered.

• Low boiling temperature components (smaller molecular weights) are used for solvents and fuels (gasoline), while high boiling temperature components with their large molecular weights are used for tar and asphalt or returned to the refining process for further cracking.

• Generally distillation of crude oil produces 40% gasoline, 20-30 % diesel fuel, 20 % heavy fuels, 10-20 % heavy oils

• Four different crude oils are shown in Table for different boiling ranges :

Main products from crude oil by distillation (%)

Hydrocarbon fuel

• Liquid hydrocarbons Cn Hm• Engine fuels are mainly mixtures of hydrocarbons, with bonds between

carbon atoms and between hydrogen and carbon atoms.• Fuels also contain small amounts of O2, N2 ,S.• Carbon atoms form four bonds in molecular structures, while hydrogen has

one bond. A saturated hydrocarbon molecule will have no double or triple carbon-to carbon bonds and will have a maximum number of hydrogen atoms. An unsaturated molecule will have double or triple carbon-to-carbon bonds

• Number of different families of hydrocarbon molecules have been identified; some of those are going to be discussed in the following slides

Prefix for common fuel components

Alkanes or Paraffins

• Parafins are chain molecules with a carbon- hydrogen combination of CnH2n+2, n being any number.

• The simplest member of this family, and the simplest of all stable hydrocarbon molecules, is methane (CH4), which is the main component of natural gas. It can be pictured as:

Alkenes

• Also called olefins• mono-olefins CnH2n or dio-olefins

CnH2n-1

• It contains one or more double carbon bonds, and therefore unsaturated.

• olefinic compounds are easily oxidized, have poor oxidation stability

• can be used in SI-engines, obtained by cracking of large molecules

• low heat content and density in the range 620 – 820 kg / m3

Naphthenes

• Also called cycloparaffins CnH2n

• Saturated molecules with single bond rings

• stable structure and low tendancy to autoignite compared to alkanes (normal paraffins).

• can be used both in SI-engines and CI-engines

• low heat content and high density (740 – 790 kg / m3)

Aromatics

• Aromatic hydrocarbons are so called because of their “aromatic” odor.

• It has unsaturated ring structure with double carbon-carbon bonds.

• It has the general chemical formula CnH2n-1 .

• can be used in SI-engines, to increase the resistance to knock

• not suitable for CI-engines due to low cetenenumber

• low heat content and high density in the range 800 – 850 kg / m3

Fuel Specifications

• Fuel composition

• Relative density (specific gravity)

• Specific heating value

• Flash point

• Viscosity

• Surface tension

• Freezing point

Fuel composition

• C and H : paraffins, naphthenes and benzene• Benzene - max allowable concentration is specified because it is highly toxic

material, the level is 5 %

• sulphur content – HC fuels contain free sulphur, hydrogen sulphide and other sulphur compounds. • it is a corrosive element that can corrode fuel lines and injection pump. It will

unite with oxygen to form sulphur dioxide, which in presence of water at low T, forms sulphurous acid. It has low ignition T, promote knock in SI engines.

Fuel composition

• Gum deposits – gasoline with unsaturated HCs forms gum in the engine, paraffin, naphthene and aromatic HCs also form some gum – it causes operating difficulties, sticking valves and piston rings, deposits in the manifold etc.

• Water - both dissolved and free water can be present in gasoline, freewateris undesirable because it can freeze and cause problems. Dissolved water is usually unavoidable during manufacture.

• Lead - for leaded and unleaded gasoline max lead content is specified, lead causes pollution and destroys catalytic converters in the exhaust system.

• Manganese - used for antiknock in gasoline (MMT), max amount is specified, 0.00025 to 0.03 gMn/L

Fuel composition

• Oxygenates - oxygenated compounds such as alcohols are used in gasoline to improve octane rating. In USA gasohol (10% ethanol contains 3.5% oxygen), TBA and methanol up to 3.5% oxygen methanol up to 5% volume, MTBE up to 15% are used.

Relative Density

• Relative density (specific gravity) is related to the measurement of the ratio of the weight of a given volume of fuel to the weight of the same volume of water, both at 21 C and 101.325 kPa

• American Petroleum Institute, also defines degrees API as,

𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝐺𝑟𝑎𝑣𝑖𝑡𝑦 =141.5

131.5 + 𝐴𝑃𝐼

• For gasoline, the relative density is around 0.72 to 0.78 - which is equivalent to an API range of 65 to 50

ρ = 700 −800 [kg/m3 ]

for unleaded gasoline this value is higher due to the aromatics

• For diesel fuel, ρ = 830 − 950 [kg/m3]

Flash Point

• Flash point is the lowest temperature of a sample at which the fuel vapour starts to ignite when in contact with a flame (ignition source).

• Marcusson method – fuel container is slowly heated, while the fuel vapour is in contact with an open flame – T is measured

• For gasoline it is 25 C, diesel fuel 35 C and heavy diesel 65 C

• Viscosity is an important parameter for CI engines, also influences fuel metering orifices.

• The lower the viscosity, smaller the diameter of the droplets in the spray.

• Below certain limits, low viscosity increases the leaks in the fuel system.

• It is a strong function of T – must be given at certain T Value

Viscosity and freezing point

• Freezing point the precipitation of paraffin crystals in winter can lead to clogged filters. It can be prevented by either removing paraffinsfrom the fuel or adding flow improvers (additives).

• For gasoline freezing point is –65 C and for diesel fuel –10 C

• Surface tension is a parameter which effects the formation of fuel droplets in sprays

• The lower the value, smaller the droplet diameter

• diesel fuel 0.023 – 0.032 N/m

• gasoline 0.019 – 0.023 N/m

Fuel specification

Fuel Specifications for Gasoline

• Volatility

• Antiknock quality

Gasoline Volatility

• For gasoline it is not possible to indicate a single value of evaporation T or vapor pressure.

• Gasoline contains large number of compounds - up to about 400

• It has a smooth distillation curve - with good fractionation efficiency

Gasoline Volatility

• Low fractionation efficiency effects engine performance at different operating conditions :

• if distillation curve is displaced downward, gasoline becomes more volatile - poor hot start, vapor lock, high evaporative losses

• %10 evaporation point: should be at low T for start up at cold temperatures - at hot weathers this may cause problems - vapor lock.

• 50% evaporation: should be slightly above 100 C at summer and slightly below 100 C at winter. For warmed up engine conditions this point is not important.

• 90% evaporation: must not be high - produces fuel film on intake manifold walls and dilutes lubricating oil. Back end of the curve must not exceed 215 OC.

• Gasoline volatility should be arranged according to weather conditions - particularly ambient T. Altitute has some minor effect due to pressure changes.

Gasoline Distillation Curve

• Gasoline having boiling point up to 70 C controls ease of starting and hot weather problems such as vapor lock

• Mid-range controls the driving in cold weathers, particularly at warm up period of engine.

• Back end of the curve contains all the heavier, high boiling point compounds and these have high heat content - they are important in improving fuel economy for fully warmed up engine.

• Some of the heavier compounds may pass into the crankcase and dilute the crankcase oil. They are not readily combusted as the lighter compounds - cause combustion chamber deposits.

Cold starting

• For SI engines to start, A/F ratio must be within the ignitable range, iein general must be between 7:1 to 20:1 by weight.

• When the engine is cold, it is difficult to ignite lean mixtures, because fuel may not vaporize sufficiently - under these conditions the mixture is richened to bring it to ignitable range.

• This is done by changing injection timing and duration or by the use of a choke with carburetted engines.

Measurement of Gasoline Volatility

• Reid vapor pressure (RVP) is a common measure of the volatility of gasoline

• it is defined as the absolute vapor pressure exerted by a liquid at 100 °F (37.8 °C) as determined by the test method ASTM-D-323.

• Oil refineries manipulate the Reid Vapor Pressure seasonally specifically to maintain gasoline engine reliability.

Antiknock Quality of Gasoline

• Knock occurs when the unburnt gases ahead of flame front (the end gases) spontaneously ignite causing a sudden rise in pressure accompanied by a characteristic pinging sound - this results in a loss of power and can lead to damage the engine.

• Combustion chamber shape, spark plug location, ignition timing, end gas temperatures, in cylinder gas motion, air-fuel ratio of the mixture, fuel specifications etc effects the occurrence of knock.

• Compression ratio of the engine also strongly effects knock. The higher the CR, the better the thermal efficiency - but the greater the tendency for knock to occur.

• Critical compression ratio - when knock starts so higher fuel octane quality is require

• Autoignition of the end gases causes a rapid increase of p, producing p waves which resonate in the combustion chamber.

• Knock results in an increase of T in the cylinder and causes a severe damage to engine components like cylinder head gasket, piston, spark plugs etc

• Octane number of the fuel is the volume percentage of iso-octane in a blend with n-heptane (PRF), that shows the same anti knock performance as test fuel tested in standard engine and standard conditions.

• There are two types of Octane numbers: • the Research Octane Numbe(RON)

• the Motor Octane Number (MON)

• Two different test conditions specifies the difference between the RON and MON

• RON correlates with low speed, mild driving conditions,

• MON relates tohigh speed, high severity conditions. Most gasolineshave higher RON than MON.

• This difference is called fuel sensitivity (=RON-MON)

• Antiknock Index = (RON + MON) / 2

Increasing Octane number• Modern gasoline contains some chemical additives designed to improve

fuel quality. These are used to raise ON, control surface ignition, reduce spark plug fouling, resist gum formation, prevent rust, reduce injection system deposits, minimize deposits in intake system, prevent valve sticking.

• ON can be increased by antiknock agents - at less expense than modifying HC composition by refinery process.

• Most effective agents are lead alkyls -• TEL - tetraethyl lead, (C2H5)4 Pb• TML - tetramethyl lead,• MMT

• Addition of about 0.8 g lead per liter, provides a gain of about 10 ON in gasoline

Different type of fuels for IC engine

• Fuels suitable for fast chemical reaction have to be used in IC engines.• Hydrocarbons in liquid form

• Alcohols (methanol, ethanol)

• LPG (propane and butane)

• Natural gas (methane)

• Hydrogen

82

Alcohols

An alcohol molecule is simply a hydrocarbon molecule with one of the hydrogen atoms replaced by a hydroxyl molecule (OH)The main alcohols used as engine fuels are:

C

H

H

H

OH

Methyl alcohol

Methanol –methyl alcohol (CH3OH) consists of methane molecule (CH4) with OH substituting one H

• can be obtained from natural gas – has near and long-term potential has high octane quality (130 RON, 95 MON)

• can be used in low-concentration (5-15 %) in gasoline to increase octane number of the mixture

• Ethanol – ethyl alcohol (C2H5OH) consists of ethane molecule (C2H6) with OH substituting one H

• has high octane number – can be used in different concentrations in gasoline

• Muh of the world uses a system known as the “E" factor to state the amount of Ethanol in any fuel mix:• About 90 % of the ethanol produced in the world is used to make "E10" or "gasohol," a

mixture of 10% ethanol and 90% gasoline.

• Any gasoline powered engine can use E10, but only specially made vehicles can run on E85, a fuel that is 85% ethanol and 15% gasoline

• Produced from biomass including:• Potato skins

• Rice

• Sugar cane

• Sugar beets

• Corn

• Sorghum

C

H

H

H

H

C

H

OH

Ethyl alcohol

Advantage of using Alcohol

1. Can be obtained from a number of sources, both natural and manufactured.

2. high octane fuel with anti-knock index numbers. High octane numbers result, at least in part, from the high flame speed of alcohol. Engines using high-octane fuel can run more efficiently by using higher compression ratios.

3. Generally less overall emissions when compared with gasoline.

4. Has high evaporative cooling (hfg) which results in a cooler intake process and compression stroke. This raises the volumetric efficiency of the engine and reduces the required work input in the compression stroke.

5. Low sulfur content in the fuel.

Disadvantage of using Alcohol1. Low energy content of the fuel. This means that almost twice as much alcohol as

gasoline must be burned to give the same energy input to the engine.• Even with the lower energy content of alcohol, engine power for a given displacement would be

about the same. This is because of the lower air-fuel ratio needed by alcohol. Alcohol contains oxygen and thus requires less air for stoichiometric combustion. More fuel can be burned with the same amount of air.

2. More aldehydes in the exhaust. If as much alcohol fuel was consumed as gasoline, aldehyde emissions would be a serious exhaust pollution problem.

3. Alcohol is much more corrosive than gasoline on copper, brass, aluminum, rubber, and many plastics

4. Poor cold weather starting characteristics due to low vapor pressure and evaporation. Alcohol-fueled engines generally have difficulty starting at temperatures below 10°C.

5. Danger of storage tank flammability due to low vapor pressure. Air can leak into storage tanks and create a combustible mixture.

6. Low flame temperatures generate less NOx, but the resulting lower exhaust temperatures take longer to heat the catalytic converter to an efficient operating temperature.

7. Many people find the strong odor of alcohol very offensive. Headaches and dizziness have been experienced when refueling an automobile

Hydrogen• Several trials have been carried out to use hydrogen in cars

• At least one automobile company (Mazda) has adapted a rotary Wankelengine to run on hydrogen fuel. It was reasoned that this is a good type of engine for this fuel.:

Advantages:

• Low emissions. Essentially no CO or HC in the exhaust as there is no carbon in the fuel. Most exhaust would be H20 and N2.

• Fuel availability. There are a number of different ways of making hydrogen, including electrolysis of water.

• Fuel leakage to environment is not a pollutant.

• High energy content per volume when stored as a liquid. This would give a large vehicle range for a given fuel tank capacity

HydrogenDisadvantage of using Hydrogen

• Heavy, bulky fuel storage, both in vehicle and at the service station.• Hydrogen can be stored either as a cryogenic liquid or as a compressed gas. If

stored as a liquid, it would have to be kept under pressure at a very low temperature. This would require a thermally super-insulated fuel tank. Storing in a gas phase would require a heavy pressure vessel with limited capacity.

• Difficult to refuel

• Poor engine volumetric efficiency. • Any time a gaseous fuel is used in an engine, the fuel will displace some of the

inlet air and poorer volumetric efficiency will result

• Fuel cost would be high at present-day technology and availability.

• High NOx emissions because of high flame temperature.

Natural Gas-Methane

• Natural gas is a mixture of components, consisting mainly of methane (60-98%) with small amounts of other hydrocarbon fuel components. In addition it contains various amounts of N2, CO2.

• It is stored as compressed natural gas (CNG) at pressures of 16 to 25 MPa, or as liquid natural gas (LNG) at pressures of 70 to 210 kPa and a temperature around -160°C.

Advantage of natural gas

• High Octane number: a very good SI engine fuel. One reason for this high octane number is a fast flame speed. Engines can operate with a high compression ratio.

• Low engine emissions. Less aldehydes than with methanol.

• Fuel is fairly abundant worldwide with much available in the United States. It can be made from coal but this would make it more costly.

Disadvantages of natural gas as an engine fuel:

1. Low energy density resulting in low engine performance.

2. Low engine volumetric efficiency because it is a gaseous fuel.

3. Need for large pressurized fuel storage tank. There is some safety concern with a pressurized fuel tank.

4. Inconsistent fuel properties.

5. Refuelling is slow process.

LPG (liquefied petroleum gas)

• Consists of propane and butane

• provides good mixture with air – cleaner combustion

• has excellent cold weather performance

• low sulphur content

• high octane number (propane 111 RON and 100 MON)

• lower density and lower heat content of LPG versus gasoline (23.5 MJ/liter for propane and 32 MJ/liter for gasoline) results a loss in fuel economy – but better combustion efficiency can reduce this loss.

Advantage of LPG

• Cost efficient. To date, using LPG (Liquefied Petroleum Gas) is 50% cheaper than regular gasoline. Because of gas price hikes, more people are becoming more open to using LPG for their vehicles.

• Reduces exhaust emissions. LPG for cars is a definite option for those who want to go green because it produces fewer emissions.

• Higher octane rating. LPG has an octane rating of 108 compared to petrol’s numbers, which vary by location

Disadvantages of natural gas as an engine fuel:

• The main disadvantage associated with the usage of LPG is to do with the storage and safety. To store LPG, you require very sturdy tanks and cylinders.• The gas has to be kept pressurized. This can also be perceived by the number of cases

LPG cylinders have exploded and resulted in serious damages to lives and property.

• In colder climates or conditions, there is a known problem related to starting due to the low vapour pressure of propane. This is known to happen in conditions with sub 32 degrees Fahrenheit temperatures.

• LPG is also known to be more expensive than CNG.

Biodiesel

• A fuel made from vegetable oils, fats, or greases — such as recycled restaurant grease.

• Biodiesel is made through a chemical process called transesterificationwhereby the glycerine is separated from the fat or vegetable oil. The processleaves behind two products -- methyl esters (the chemical name forbiodiesel) and glycerine (a valuable by-products usually sold to be used insoaps and other products).

• Much of the world uses a system known as the "B" factor to state the amount of biodiesel in any fuel mix.• 100% biodiesel is referred to as B100, 20% biodiesel, 80% petrodiesel is labeled B20,

5% biodiesel, 95% petrodiesel is labeled B5.

• Blends of 20% biodiesel and lower can be used in diesel equipment with no, or only minor modifications

Advantages:

• Produced from Renewable Resources:

• Can be Used in existing Diesel Engines: up to 20% percentage with very little modification. Increasing the percentage might require change in some of the material properties

• Biodiesel has promising lubricating properties and cetane ratings compared to low sulfur diesel fuels.

• In certain running conditions it produce less regulated emissions

Disadvantage

• Biodiesel has different solvent properties than petrodiesel, and will degrade natural rubber gaskets and hoses in vehicles

• The calorific value of biodiesel is about 37.27 MJ/kg. This is 9% lower than regular Number 2 petrodiesel.

• It can contaminated with water (soluble water)