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A heat engine is a machine whose function is to produce mechanical energy and it does so by using heat energy that is released when combustion of fuel takes place.
It is classified in two main types on the basis “where the combustion takes place”.
1. External combustion engines also called the E.C engines:
Here, as name suggests, heat energy from fuel is extracted not inside the cylinder where mechanical movement is generated but outside at different setup from where it is carried along in any medium such as air, steam or gas and passed into setup where it can be used for generating mechanical movement. Examples of this type of engine are hot air engines, steam turbines, steam engines and closed cycle gas turbine. This kind of engine is mostly used in electric power generations, ships, and driving locomotives.
2. Internal combustion engines famously known as I.C engines:
It can be easily understood from the name that heat energy of fuel is extracted inside the cylinder from where mechanical movement originates.
Here the mechanical energy is generated by force on nozzle, blades of turbines or pistons. They are arranged in such a way that when fuel is burnt inside combustion chamber the gases so produced as result of this action having very high pressure and very high temperature creates a force that directly leads to the their movement.
From the development point of view we can say that J.J.E Lenior was the one who developed the first practically okay engine in 1860 and after that many different version were experimented mostly having power of around 4.5 kw and efficiency near 5%. otto-langen is given credit for developing a four stroke cycle engine in 1876. The efficiency of engine was nearly around 11%. It worked on spark ignition system. In 1892 rudolf diesel came with the compression ignition engine which was more efficient than spark ignition engines.
1.2.1 Classification of I.C. Engines.
It is an internal combustion heat engine where heat energy, produced by spraying fuel on compressed air having a high temperature that is above the self-ignition temperature of fuel inside the cylinder, is converted in to mechanical work. Piston is arranged inside the cylinder that produces this mechanical work in response to combustion and expansion of air inside the cylinder.
Diesel engine works on both 2 stroke and 4 stroke cycle. The main difference between diesel and petrol engine is that diesel works on the concept of constant pressure heat addition while petrol works on the concept of constant volume heat addition. For an engine to work on constant pressure heat addition concept it needs fuel which has low self-ignition temperature. And the fact that only air is compressed inside the cylinder is the reason for high compression ratio of diesel engine. They lie in the range of 14-22.
The four important processes of a diesel engine are intake of air, compression of the air to temperature that is above the self-ignition temperature of fuel, combustion inside the cylinder by spraying fuel on the compressed air and finally letting out the gases from cylinder after combustion. These four processes are repeated in cycle to make the engine run continuously. These four processes can be done with two strokes of piston (one revolution of crankshaft) or four strokes of the piston (two revolution of crankshaft).
Lets understand the four stroke processes briefly because we are going to perform experiment on 4-stroke engine. During first stroke piston moves down creating space for air to come in. now when piston moves upward it compress air within the cylinder. When piston reaches at the top fuel is sprayed in the cylinder. This leads to combustion and downward movement of piston. After reaching bottom piston moves upward removing the exhaust gas from cylinder. And again when piston moves down fresh air is taken in cylinder and processes goes on. The up and down movement (linear motion) of piston is converted in to rotary motion through crankshaft which is connected to the piston. Please refer to the diagram below.
2.3 FUEL INJECTION
The injection of fuel to the cylinder is very critical processes. If done with accurate timing and injection pressure it can lead to enhanced performance of the engine. The injection pressure given to the fuel by injector is typically 7€ª106 to 7€ª107 pa. The accurate time for fuel injection is when piston is about to reach the top of cylinder. When fuel is injected inside it is partly combusted as constant volume and then as piston moves down the remaining part is combusted as pressure constant processes.
2.4 PROS AND CONS OF DIESEL ENGINE
The diesel engine is far more superior to the gasoline engine in terms of efficiency. They do not make noise and are very low on maintenance requirement when compared to gasoline engines. Its reliability and ruggedness is more. As fuel leads to combustion due to low self-ignition temperature no spark plugs are required which leads to lower cost of maintaining. Cost of fuel is lower, around 30% to 40% than gas engines. Another major advantage it gives over gasoline engine is by producing low waste in exhaust and cooling
Major disadvantages of diesel engine are its high weight to horsepower ratio and difficulty to make them start when they are in cold weather area.
DIESEL FUEL AND ADDITIVES
Any liquid that can be utilized to operate diesel engine is called as diesel fuel. Mainly derived from following four sources.
Diesel fuel has been divided into three major groups by ASTM (The American society for testing and materials), which depends on the various uses of diesel engines. They are:
No. 1-D for frequent load and speed changing engines.
No. 2-D for engine with constant speed but high loads.
No. 3-D for low and medium speed engines that operate under sustained loads.
3.1 DESIRED QUALITIES OF DIESEL FUEL
Keeping in mind the functioning of diesel engine that are few important and critical qualities that a liquid must have to serve as diesel fuel. They are:
3.2 STANDARD SPECIFICATION OF DIESEL FUEL
Depending upon intention of use, diesel fuel is available in various grades. Diesel fuel is a mixture of different crude oil derived substances, all with their own physical and chemical properties, such as paraffins, isoparaffins, napthenes, olefins and aromatic hydrocarbons. Diesel fuel has to work in various kinds of engine types, having difference in conditions of operation and cycles of duty, and range of technology of fuel system, temperatures of engine and pressures of fuel system. It must suit a wide range of different climates. The balanced properties of each grade of diesel fuel are important to give good performance over an extremely various situation .The most common in use guidelines for diesel fuel are given by ASTM International. ASTM specifications are created after taking into consideration, based on the wide range of experience and cooperativeness of diesel fuels producer, diesel engines manufacturer and fuel systems (and users of both), and other important officials like state fuel quality regulators.
3.3 IMPORTANT PROPERTIES OF FUEL
3.4 DIFFERENT TYPES AND FUNCTIONS OF ADDITIVES
Diesel fuel properties are met and maintained by petroleum industry by taking the use of number of commercial diesel fuel additives.
Fuel components and additives are different from each other. Firstly Fuel Components are hydrocarbon classes like aromatic, iso-paraffin and naphthene. They basically sum up the volume of the fuel. While Additives are added to fuel in at very less amounts, generally at the ppm level, and is of no significance fuel volume. There are different types of additives that are used to improve fuel in different ways and to overcome different problems. Following table give different types of additives and their functions.
Table showing different types and function of additives.
Type of Additive
Cetane number improver
Improves ignition quality by raising cetane number, better starts, reduces white smoke
Improves lubricity, better injector & pump lubrication
Extend storage life, inhibit oxidation, reduce gum and precipitate formation
Inhibit oxidation &extend storage life
Deactivate copper compounds in fuel, thereby promoting longer storage life
Pour point depressants
Low temperature operability, improve cold flow properties
Promote more complete combustion reduce exhaust smoke
Reduce formation of rust in fuel systems & storage tanks
Used to increase the rate of water separation from the fuel
Having very high oxidizing capability Hydrogen peroxide (h2o2) is one of the strongest reactive oxidizer that exists. Naturally, it is synthesized as the by-product of oxidative metabolism in nearly all-living organisms. It is mainly used as a propellant in rocketry, as bleach, as an antiseptic and as an oxidizer. It has IUPAC name of Di-hydrogen dioxide and is also known as Dioxidane.
Molecular diagram of hydrogen peroxide
4.1 IMPORTANT PROPERTIES OF H2O2:
1. Hydrogen peroxide has a Molar mass of 34.0147 g/mol
2. It appears colorless in solution and otherwise has a very light blue color.
3. H2O2 has density of 1.463 g/cm3
4. Melting point of -.43 oc. and boiling point of 150.2 oc.
5. It has more viscosity than h2o.
6.It has calorific value of 2700 kJ/kg.
7. Has dipole moment of 2.13 debye and refractive index of 1.33 (same as that of water)
8. It has specific heat capacity of 1.267 J/kg (gas) and of 2.619 J/kg (liquid)
4.2 HYDROGEN PEROXIDE AS AN ADDITIVE:
One important reaction of hydrogen peroxide is its spontaneous exothermic decomposition into oxygen and water. The reactions is:
2 H2O2 ® 2 H2O + O2
It has: 1. Standard enthalpy of reaction of -98.4 kJ/mol
2. Gibbs free energy of -118.7 kJ/mol
3. Change of entropy of 71 J/mol
Because of this property of hydrogen peroxide it is used as propellant in rocket. Here high-test peroxide (hydrogen peroxide with concentration of around 90%) is used. The H2O2 decomposes into steam and oxygen.
According to me same concept can be applied to diesel engine as well. Where adding small amount of hydrogen peroxide to the diesel fuel can improve ignition of diesel fuel inside combustion chamber by providing additional oxygen and energy when it decomposes. And steam thus produced will easily move out along the exhaust gases.
To conduct experiment using 4 stroke, 2 cylinder diesel engine to study the effects of addition of hydrogen peroxide to the diesel fuel. And compare the performance of three different sample fuel where the first one is 100% diesel, second is 95% diesel + 5% hydrogen peroxide and third is 90% diesel + 10% hydrogen peroxide.
To calculate following parameters for three fuel samples:
Brake power (BP).
Brake mean effective pressure (Pbm)
Fuel consumed (Qf)
Heat energy produced by fuel (Hf)
Brake specific fuel consumption (BSFC)
Brake thermal efficiency (¨bt)
Air fuel ratio (A/F)
5.3 EXPERIMENTAL SETUP:
Diesel engine has two cylinders and is four stroke, water-cooled engine. Dynamometer that is a rope brake type has been provided with loading sensors. Different rota-meters has been arranged to calculate flow of water to calorimeter of exhaust gas and to the engine jacket. Setup is equipped with temperature sensors, air tank and fuel tank for supply.
Software has been programmed to collect data. It provides experiment performer to log-in data and store and print them. This software allows tabulation and comparison of data collected.
Now lets discuss about the dynamometer mentioned above. It has brake drum, load cell, and arrangement of cooling down water. It is so coupled with the shat of the engine that load can be changed using rotation of wheel that increases the tension of the drum.
Another important part of the setup is facility provided to measure the heat energy gone along with exhaust gases. Calorific measuring meter is equipped with jacket of the cooling water and shell that is in central with baffles. Water is made to flow against in indirect contact with gas that comes from exhaust and there is a rota-meter and valve to control the rate of flow of this water. So using heat can be measured that is going out as a waste with gases that comes from exhaust.
There also is a provision made for getting p-v and p-‘ graphs. These works based on the sensors. Sensors that are stored in combustion chamber and aligned along the shaft that gives the output motion that has been produced by engine. These sensors provide the software the data of different pressure and angle of crank. And then we directly get graphs on the computer. But sadly these sensors have been damaged and cannot be used. So we are not able to get these graphs which are essential part of performance analysis.
5.4 EXPERIMENTAL PROCEDURE:
First of all three different samples of fuels are made. Sample 1 is pure diesel. Sample 2 is 5% hydrogen peroxide and 95% diesel. Sample 3 is 10% hydrogen peroxide and 90% diesel.
All the pre-checks of the engine are conducted such as SAE 20w40 oil is filled in the oil sump up to needed level using a stick that is made specially for this purpose, data cable is connecting unit of interfering with the computer, flow of water is set accordingly through rota-meters.
Filling of the fuel sample in the fuel tank.
Starting engine with the help of lever that is for decompressing. Lifting this lever while turning flywheel at high speed taking use of handle leads to smooth starting of engine. Run the engine for like say 2 min before any thing to be done because it needs time to stabilization.
Now loading of the diesel engine is done with help of dynamometer. Here we will try and set four different loads for a sample of fuel. Firstly zero kg then eight kg after that 16 kg and finally 24 kg.
Readings are noted down or you may say logged in the computer for every load and saved.
After completion of the experiment for fuel 1 same procedure is followed for other two samples.
After the readings and information of all samples are collected stop the engine only after reducing load on engine.
Finally close the supply of water that is used for cooling and stop the fuel supply.
5.5 IMPORTANT SPECIFICATIONS OF ENGINE:
14 horse power engine
Diameter of bore is 87.5 mm
Length of stroke is 110 mm
Length of arm acting on dynamometer is 0.165m
Density of air is taken as 1.21 kg/m3
Gravitational acceleration is 9.81 m/s2
Surface area of piston is 6.01*10-3 m2
Volume swept by cylinder per second is .0165 m3/sec
5.6 FORMULAE USED:
Please note formulae have been written after calculating all constant and known values as specific numerical constant so as to get clear picture of what and how different variables affect the values of performance indicators. And also that following set of formula apply for sample 1 only and similarly formulae for sample 2 and 3 were calculated separately.
Brake-power (in kw):
m is mass of load acting on dynamometer (kg)
N is revolution per minute of shaft
Break mean effective pressure (in N/m2):
Fuel consumed by engine (in kg/s):
X is volume of fuel consumed (in ml)
T is time taken to consume X ml of fuel (in seconds)
Air fuel ratio:
Qa is flow rate of air intake by engine (in m3/s)
Brake specific fuel consumption (in kg/kw-s):
Heat supplied by fuel (in kw):
Brake thermal efficiency (in %):
Volumetric efficiency (in %):
5.8 ANALYSIS AND COMPARISION OF PERFORMANCE:
GRAPH: LOAD VS BRAKE POWER
From above graph we can say that all the 3 samples of fuel are able to give same brake power output. This helps us to confirm that 2 experimental fuel are able to provide same output as that provided by original fuel.
GRAPH: LOAD VS BSFC
From the graph we can observe that sample 2 has higher BSFC then other 2 samples at low loads. But as the load is increased sample 2 has slightly lower BSFC than other two samples. While sample 3 gives you lower BSFC at low loads and same BSFC as the sample 1 at higher loads.
GRAPH: LOAD VS BRAKE THERMAL EFFICIENCY
From graph above, it is clearly visible that sample 2 and sample 3 provides higher efficiency than the original sample 1. And it is also important to note that there is not much vast difference between efficiency of sample 1 and sample 2
The experiment was performed on the 4-stroke, vertical, 2-cylinder diesel engine. It was maintained at constant rpm of 1498 and 50 ml of fuel was consumed at each load. Four load conditions were decided to perform experiment on 3 samples of fuel keeping in mind the capability of engine. The 4 conditions were 0, 8, 16, and 24 kg.
The positives that we can take from the experiment performed are that we are able to produce same output result in terms of output power at output shaft though the heating value of sample fuel 2 and 3 are lower than that of sample 1. This is the reason we are able to show increase in brake thermal efficiency obtained by sample fuel 2 and 3 than that obtained by sample 1. But the most important conclusion that I think from the experiment is that there is slight decrease in BSFC of sample fuel 2 at high load. Due to limitation of experimental conditions we cannot check the result for load above 25 kg. I believe that this result has originated from the fact that hydrogen peroxide provides that additional oxygen and energy when it decomposes exothermically to give steam and oxygen.
The thing that hampers the proposition of hydrogen peroxide as an additive for diesel fuel is its storage problem. A research is needed on the feasibility of storing hydrogen peroxide separately than the diesel in engine and spraying it through different injection system than that of diesel because there could be possibility when hydrogen peroxide in the fuel tank it may decompose itself without aid of compression temperature in combustion chamber in long-term storage. The cost factor also needed to be taken into account. The other few things that are kind of inconclusive and needs further research on them are how does steam produced by decomposition reaction affects the engine on long run and what amount of hydrogen peroxide is optimum for the engine.
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