Comparative analysis of commonly available fuels

Objective:-

To study the different properties of the fuel and on the basis of their property, write an analysis which will help people in determining the right fuel for their vehicle.

Considerations:-

Only those fuels are considered which are commercially available all over the world.

Petrol (Gasoline):-

A jar of Gasoline

Specific gravity :-

The specific gravity (or relative density) of gasoline ranges from 0.71–0.77 (0.026 lb/in3; 719.7 kg/m3; 6.073 lb/US gal; 7.29 lb/imp gal), higher densities having a greater volume of aromatics.Color:-

Gasoline is mostly clear with a little yellow color.

Additives:-

Methylcyclopentadienyl manganese tricarbonyl (MMT) has been used for many years in Canada and recently in Australia to boost octane. It also helps old cars designed for leaded fuel run on unleaded fuel without need for additives to prevent valve problems. The only way you benefit from a certain grade of fuel is to have ignition timing set accordingly. Typical "octane booster" gasoline additives include MTBE, ETBE, isooctane and toluene. Lead in the form of tetra-ethyl lead was once a common additive.

Mixing alcohol with gasoline produces gasohol. Advantages of fuel blends are that alcohol tends to increase the octane rating, which is particularly important in unleaded fuel, and reduce carbon monoxide (CO) emissions from the engine.

Burning Equation:-

Gasoline is a mixture of chemicals, so a single equation couldn’t possibly show it. Here’s

A balanced equation for octane, a common constituent of gasoline assuming complete combustion.

C8H18 + 25 O2 16 CO2 + 18 H2O

One H-H bond has 436 kj/mole

One C-H bond has 413 KJ/Mole

While one O=O bond has 498 KJ/Mole.

So in breaking 18 C-H bonds we require 7434 KJ/Mole of energy

To break 25 O=O bonds we need 12450 KJ/Mole.

So total of 19884 KJ/Mole is required to do all the decomposition.

The C=O double bond in carbon dioxide (O=C=O) has a bond energy of 360 KJ/Mole so total of 11520 KJ/Mole

Plus 13176 of bond formed in water.

So total of 24696 KJ/Mole of energy is released while forming bonds.

So we get net energy of 4812 KJ/Mole of energy for Gasoline.

Diesel:-

The average chemical formula for common diesel fuel is C12H23

Color: - Light Yellow (highway)Blue (Marine, construction, Agriculture [off highway])

Density:-

The density of diesel fuel oil (20 to 60) at 15 degrees Celsius is 820 to 950 kg/m 3. In other words, it has from 82 to 95 percent the density of water, or specific gravity (relative to water) of 0.82 to 0.95.

Additives:-

The only thing we ever put in our fuel is automatic transmission fluid. We put a quart in the fuel about every third tank because it is high detergent and helps keep the nozzles clean. Two independent studies rated Opti-Lube XPD as the best diesel fuel additive.

Alcohol also has been used in diesel engines. In this case, the alcohol may be blended with diesel fuel to produce diesohol, or the alcohol may be added to the air intake of the engine. The primary function of the system is to cool the turbocharged air (using the latent heat), and thereby to increase the volumetric efficiency of the engine and produce more output power.

Composition:-

You realize that Diesel fuel is not a single compound, but rather a mixture of hydrocarbons. The "average" is C12H23. Diesel goes from C10H20 to C15H28.

The chemical equation for the complete combustion of Diesel fuel would then be:

4C12H23 + 71O2 48CO2 + 46H2O

Of course, in the real world we don't get the complete combustion of Diesel fuel, so that what comes out the exhaust is a widely varying mixture of substances from elemental carbon to potentially unburned fuel.

LPG:-

LPG is essentially compressed propane gas.

Commercial Usage of LPG

LPG combustion:

C4H10 + O2  CO2 + H2OAnalysis: C = 4; H = 10; O = 5 + 8 = 13

So the equation will be: C4H10 + 61/2O2  4CO2 + 5H2O

Multiplied by 2:2C4H10 + 13O2   8CO2 + 10H2O

Household LPG cylinder

Color:-

Golden Yellow

Density:-

The density of compressed liquid propane at 25 °C is 0.493 g/cm3

Additives:-

LPG propane additive, LPG cutting fuel additive, LPG bulk tank cleaner are used to

Increase the life and efficiency.

Methanol:-

Aem Water Methanol Injection Kit 1997 Nissan 240Sx

Color:-

Colorless liquid

Additives:-

Gasoline is added into Methanol to increase its lubricity.

M2â„¢ Upper Lube: Leaves a thin film of lubrication to protect against corrosion between races. It also protects valves, guides, cylinder walls, fuel pumps, and aluminum fuel systems for methanol powered engines. Extends pump life. Virtually eliminates white powder residue from the interaction of Methanol and aluminum fittings. It also allows fuel to be left in fuel lines for longer than normal.

M2â„¢ Upper Lube with Candy Scent

Identical to the M2 Upper Lube, this has a Strawberry Candy Scent added. This additional reduces the burning sensation form Exhaust Methanol fumes. Reduction of such irritation enables drivers and work crew to be able to work longer, drive better.

Burning Equation:-

2CH3OH + 302 2CO2 + 4H2O

Ethanol:-

Agriculture and Ethanol

Burning Equation:-2C8H18+2C2H6O+31O220CO2+24H2O

Energy:-

Color:-Colorless liquid

Additives:-

Quickleen is mostly added in Ethanol.

Relationship of Ethanol and Economy as shown by NY Times

CNG (Compressed Natural Gas):-

A CNG cylinder in TOYOTA

Chemical Formula:-

It is essentially methane which is CH4.

Burning Equation:-

CH4 + 2O2 CO2 + 2H2O

Density:-

The density of CNG is 8 lbs/gallon.

Color:-

It is colorless.

Additives:-

Phosphorus for anti-wear

Modifications in an AUDI engine for CNG operation

Effects of using one fuel in other engine:-

Following are the methods for converting one fuel engine to be run by another fuel:

Diesel to LPG:-

Reduction of Compression Ratio:-

Diesels often run at a compression ratio of roughly 16-1 (one of the reasons they are more economical) whereas Petrol and LPG engines need a ratio of around 10-1.

Introduction of Spark:-

We need to provide diesel engine with a spark to make it run on LPG or Petrol.

Diesel to Gasoline:-

When you use gasoline in a Diesel engine the gasoline does not ignite properly and burns up too quickly and the result is very low power output.

The result is slightly more than low power

You either blow the engine, or wreck the pump.

Since gasoline is designed to be resistant to self-ignition, gasoline in a diesel engine either won't ignite or will ignite at the wrong time.

Diesel fuel acts as a lubricant for the fuel pump so the Gasoline will, over time, destroy any seals in said pump.

Gasoline to Diesel:-

Putting diesel in a petrol engine is not recommended.

On older engines, it can clog the carburetor or injectors

Diesel and CNG:-

There are a lot of Changes to be made if CNG is to be used in Diesel engine.The Cylinder head need to be changed as we need to install the Spark plugs instead of the Fuel Injectors (Diesel).

We need to reduce the compression Ration from 21:1 (approx) to 9: 1(for CNG).We need to install a firing / Ignition device to send spark to the spark plug. We need to change the Manifold or modify the existing manifold to plumb the gas (CNG) into the inlet manifold.

We need to install the Venturi to control the gas / air mixture.Then of course we need to change the piston / cylinder head etc and all these changes will involve a complete engine change. 

You will also need a timing device for the ignition system.

But to do that we need

To improve cooling system efficiency

Engine oil cooler

New valve seats, guides and seals

New pistons and rings

Engine compression must be lowered

May need a new camshaft

Ignition system must be installed

Cylinder head modifications are needed to install spark plugs

Custom cam or crankshaft position sensors must be made.

COMPARISON:-

Storage:-

1) Diesel is stored in yellow container in comparison with Gasoline or Kerosene which are kept in Blue and Red containers.

2) LPG is stored in spherical containers.3) CNG is stored in cylindrical cylinder due to high forces it exerts on the walls of

containers!4) Ethanol needs to be stored in a sealed glass or plastic container and kept away from

sources of flame/sparks (e.g. in a metal cabinet). Larger quantities are usually stored in a metal tank, grounded to prevent static discharge causing sparks, and vented to prevent pressure build up if the tank gets too warm.

5) Same goes for methanol.

Production:-

1) The basic steps for large scale production of ethanol are: microbial (yeast) fermentation of sugars, distillation, dehydration (requirements vary, see Ethanol fuel mixtures, below), and denaturing (optional). Prior to fermentation, some crops require saccharification or hydrolysis of carbohydrates such as cellulose and starch into sugars. Saccharification of

cellulose is called cellulolysis (see cellulosic ethanol). Enzymes are used to convert starch into sugar.

2) Gasoline is produced in oil refineries. Material that is separated from crude oil via distillation, called virgin or straight-run gasoline, does not meet the required specs for modern engines (in particular octane rating; see below), but will form part of the blend.

3) Same goes for Diesel.4) Methanol can be produced using a number of raw materials (feedstock), but its

production with natural gas is preferred. The methane in natural gas reacts with steam in a reaction called steam-methane reforming; the resultant synthesis gas then reacts with a catalyst to produce methanol and water vapor.

5) LPG is produced during the petrol chemical distilling process of crude oil.6) It is produced commonly from natural gas (Methane). CNG is also produced from sewage

treatment plants.

Economy:-

1) Diesel is generally cheaper than Gasoline due to its lower refining. But in Pakistan due to its high demand, its expensive than petrol.

2) CNG is cheaper than both of them. It also has lower maintenance costs. Natural gas is cheaper per equivalent gallon than gasoline (an average of 15% to 50% less than gasoline).

3) LPG is as much more expensive than diesel in Pakistan due to no production, but in foreign market its generally cheaper but due to its high demand there’s an increasing trend in its prices.

4) While methanol and ethanol are expensive due to comparatively new technology.

Safety:-

1) Methanol and ethanol are highly flammable and are hence placed away from any area that is suspicious of any kind of spark.

2) Gasoline is highly flammable too.3) Diesel is also flammable but less as compared to Gasoline.4) LPG is also highly explosive.5) CNG is comparatively safer due to its high burning point.

Efficiency:-

1) Modern gasoline engines have an average efficiency of about 18% to 20% when used to power a car. In other words, of the total heat energy of gasoline, about 80% is ejected as heat from the exhaust, as mechanical sound energy, or consumed by the motor i.e. frictional losses and heat loss inside the cylinder. Toyota targeting thermal efficiency of more than 45% for next-generation gasoline engines for hybrid.

2) Engines using the Diesel cycle are usually more efficient. Since diesel engines use much higher compression ratios (the heat of compression is used to ignite the slow-burning diesel fuel), that higher ratio more than compensates for the lower intrinsic cycle efficiency, and allows the diesel engine to be more efficient. The most efficient type, direct injection Diesels, are able to reach an efficiency of about 40% in the engine speed range of idle to about 1,800 rpm. Beyond this speed, efficiency begins to decline due to air pumping losses.

3) CNG has a slight advantage of efficiency over gasoline. Its efficiency is around 25-30%.

4) LPG has average thermal efficiency of 35%. 40.23% is also achieved in laboratories.5) Methanol has thermal efficiency of around 45%.

Parameters that define the fuel:-

Here are the parameters by which any fuel can be judged efficient or inefficient:-

Octane Rating:-

Octane number depends upon:

1) Fuel Structure.2) Additives.3) Ignition Control.4) Combustion Chamber Design.5) Valve Timing.6) Carburetors and Injectors Design.7) Transmission-Engine Relationship.

Gasoline RON 91MON 92AKI 91.5

Diesel RON 20MON Diesel is judged more on cetane

number than octane numberAKIMethanol RON 109

MON 89AKI 99

Ethanol RON 109MON 90AKI 99.5

LPG RON 112MON 97AKI 104.5

CNG RON 130MONAKI

Knocking:-

Knocking (also called knock, detonation, spark knock, pinging or pinking) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front

Gasoline:-

Gasoline, when used in high compression internal combustion engines, has a tendency to auto ignite (detonation) causing a damaging "engine knocking" (also called "pinging" or "pinking") noise.

Diesel:-

Knocking is more or less unavoidable in diesel engines, where fuel is injected into highly compressed air towards the end of the compression stroke.

There is a short lag between the fuel being injected and combustion starting. By this time there is already a quantity of fuel in the combustion chamber which will ignite first in areas of greater oxygen density prior to the combustion of the complete charge. This sudden increase in pressure and temperature causes the distinctive diesel 'knock' or 'clatter', some of which must be allowed for in the engine design.

Careful design of the injector pump, fuel injector, combustion chamber, piston crown and cylinder head can reduce knocking greatly, and modern engines using electronic common rail injection have very low levels of knock. Engines using indirect injection generally have lower levels of knock than direct injection engine, due to the greater dispersal of oxygen in the combustion chamber and lower injection pressures providing a more complete mixing of fuel and air.

Diesels actually don't suffer exactly the same "knock" as gas engines since the cause is known to be only the very fast rate of pressure rise, not unstable combustion. Diesel fuels are actually very prone to knock in gas engines but in the diesel engine there is no time for knock to occur because the fuel is only oxidized during the expansion cycle.

In the gas engine the fuel is slowly oxidizing all the while it is being compressed before the spark. This allows for changes to occur in the structure/makeup of the molecules before the very critical period of high temp/pressure.

Methanol:-

It has same knocking problems as of gasoline as it is added into it. Moreover it absorbs water readily causing engine knock to be suppressed.

Ethanol:-

Due to its high octane number it’s less prone to knocking.

LPG:-

LPG is supposed to have a much higher octane rating than petrol so knocking would only be an issue if it was running too lean.

CNG:-

Due to its anti-knock property, CNG can be safely used in engines with a compression ratio as high as 12:1 compared to normal gasoline (ranges from 7.5:1 to 10:1). At these high compression ratios, natural gas-fuelled engines have higher thermal efficiencies than those fuelled by gasoline.

Volatility:-

Volatility is the tendency of a substance to escape to gaseous form from its liquid form at a given temperature.

Gasoline:-

Gasoline is more volatile than diesel oil. This property is also because of the additives that are put into it. REID VAPOR PRESSURE (RVP) is used to measure the vapor pressure for petrol.

Diesel:-

Diesel is highly volatile fuel.

Methanol:-

Methanol has low volatility due to hydrogen bonding between its molecules.

Ethanol:-

Volatility of ethanol is significantly high due to the absence of hydrogen bonding.

LPG:-

It is highly volatile when exposed to atmosphere.

CNG:-

It is also volatile being a gas.

Compression Ratios:-

The ratio is calculated by the following formula:

CR = πb 2 s+V c

Vc

Where

b= cylinder bore (diameter)

S= piston stroke length

Vc= clearance volume.

It is the volume of the combustion chamber (including head gasket). This is the minimum volume of the space at the end of the compression stroke, i.e. when the piston reaches top dead center (TDC). Because of the complex shape of this space, it is usually measured directly rather than calculated.

Gasoline:-

Due to pinging (detonation), the compression ratio in a gasoline or petrol-powered engine will usually not be much higher than 10:1.

With the addition of variable valve timing and knock sensors to delay ignition timing, it is possible to manufacture gasoline engines with compression ratios of over 11:1 that can use 87 MON (octane rating) fuel.

For turbocharged and supercharged it is usually around 9.32:1.

While for racing motorcycles it is around 12:1 to 14:1.

Diesel:-

CR will customarily exceed 14:1. Ratios over 22:1 are common. The appropriate compression ratio depends on the design of the cylinder head. The figure is usually between 14:1 and 16:1 for direct injection engines and between 18:1 and 23:1 for indirect injection engines.

Methanol:-

Ethanol and methanol can take significantly higher compression ratios than gasoline. Racing engines burning methanol and ethanol fuel often incorporate a CR of 14.5-16:1, with F1 engines coming closer to 17:1(which is very critical for maximizing volumetric/fuel efficiency at around 18000 rpm)

Ethanol:-

Ethanol and methanol can take significantly higher compression ratios than gasoline. Racing engines burning methanol and ethanol fuel often incorporate a CR of 14.5-16:1, with F1 engines coming closer to 17:1(which is very critical for maximizing volumetric/fuel efficiency at around 18000 rpm).

LPG:-

Due to high octane rating, compression ratio of as much as 10.5:1 is usually deployed in LPG engines.

CNG:-

CNG engines usually have CR around 13:1. Honda GX engine has CR of 12.5. while it can vary from 12:1 to 14:1.

Boiling Points:-

Gasoline:-

Boiling Point of Gasoline is 35-204.4oC at atmospheric conditions. Generally varies due to additives added into it.

Diesel:-

154.3oC

Methanol:-

65oC

Ethanol:-

78oC

LPG:-

-42.6oC

CNG:-

-161.6oC

Melting Points:-

Gasoline:-

-57C

Diesel:-

-30 to 18°C

Methanol:-

-98 °CEthanol:-

−114 °C

LPG:-

-187.7oC

CNG:-

-182.5 °C

Auto-Ignition Temperature:-

The auto ignition temperature or kindling point of a substance is the lowest temperature at which it will spontaneously ignite in a normal atmosphere without an external source of ignition, such as a flame or spark.

Gasoline:-

246ºC

Diesel:-

210ºC

Methanol:-

385 °C

Ethanol:-

363ºC

LPG:-

The temperature required to ignite LPG in air is around 500°C.

CNG:-

732ºC

Flash Point:-

The flash point of a volatile liquid is the lowest temperature at which it can vaporize to form an ignitable mixture in air. Measuring a liquid's flash point requires an ignition source. At the flash point, the vapor may cease to burn when the source of ignition is removed.

Gasoline:-

-43ºC

Diesel:-

62ºC

Methanol:-

11–12 °C

Ethanol:-

16.6ºC

LPG:-

-104oC

CNG:-

-184.4ºC

Energy Content:-

Gasoline:-

Gasoline contains about 35 MJ/L or 47 MJ/Kg (9.7 kW·h/L, 132 MJ/US gal, 36.6 kWh/US gal) (higher heating value) or 13 kWh/kg, or 125000 BTU/Gallon. This is an average; gasoline blends differ, and therefore actual energy content varies from season to season and from batch to batch.

Diesel:-

We get around 38.6 MJ/L or 48 MJ/Kg of energy for diesel, if it is burnt completely.

LPG:-

26.8 MJ/L or 46 MJ/Kg

Methanol:-

Methanol contains about 17.9 MJ/L or 19.9 MJ/Kg of energy

Ethanol:- It has energy of around 21.2 MJ/L.

CNG:-

It releases about 22,800 BTU/gal of heat.

Timing:-

Gasoline:-

When you advance to far, peak cylinder pressure occurs when the piston is still on the compression stroke = detonation! on the other side, when you retard timing you get better top end power b/c of this reason: the faster an engine revs, the more timing it needs to completely burn the fuel in the cylinder (this can be up to 25 degrees more than base timing!)

Diesel:-

The timing of the combustion process must be precisely controlled to provide low emissions with optimum fuel efficiency. This timing is determined by the fuel injection timing plus the short time period between the start of fuel injection and the auto ignition, called the ignition delay.

Methanol:-

A methanol engine has highly advanced timing, going as much prior to TDC as 35 degrees. About 6 degrees advanced combustion is in practice for methanol.

The ignition timing must be advanced more than for gas when burning methanol. If the timing isn't advanced enough, some of the methanol will go unburned and little will be gained. Modifications to the point lobe on the camshaft may need to be made in order to achieve the full ignition timing setting. Methanol also requires a hotter spark.

Ethanol:-

In order to take advantage of the great antiknock qualities that alcohol fuel provides, you'll have to advance the engine's ignition timing by turning the distributor housing opposite to the direction in which the rotor spins (the housing is held in place by a bolted clamp).

Normally, an engine using gasoline has its timing set so the spark occurs at anywhere from 8 deg BTDC (Before Top Dead Center) to TDC (Top Dead Center). Since alcohol has a higher "octane" rating, you can advance the timing considerably more than this. (In the case of MOTHER's truck, we adjusted it to operate at approximately 22 deg BTDC without any sign of pre-ignition, even under load.) Of course, care should be taken when you adjust the timing on your vehicle, since a 22 deg advance might be excessive for your car. Remember, it's not safe to

be just short of detonation, since inaudible knocking can also damage the engine ... the best procedure is to set the distributor timing at least two degrees retarded from the point of detonation.

LPG:-

It can tolerate up to 10 degrees of advance timing. 8 deg BTDC and a 0.7mm gap on the plugs. LPG needs more initial advance at lower RPM, but less total advance at higher RPM.

CNG:-

3 to 16 degrees advanced.