 Myself Dr. Nitin Ramopadhyay working as assistant professor in Department of Humanities and Sciences. Today we will learn the topic fuel and a particular beat from that topic is comparison of types of fuels. This is the learning outcome for today's session. At the end of this session students will be able to describe definition, types and comparison of fuel. This is the content we are going to learn. First we will see definition of fuel, then we will learn what are the different types of fuels and finally we will learn how the fuels are compared over each other by referring the important characteristics of the fuel. Now what do you mean by the material fuel? Fuels are the materials which are used as a source of energy to perform different kind of domestic, industrial and transportation work. The substance which essentially consists of carbon as a major ingredient, which on burning in presence of air combines with atmospheric oxygen and forms corresponding products with the evolution of heat. The evolved heat is used for different kinds of work. So the fuel is a material which is rich in carbon on burning in open atmosphere. It combines with the atmospheric oxygen, forms the corresponding products along with the evolution of heat and that evolved heat is used for different kinds of work. The same here represented with chemical reaction. Now these are the types of fuels. There are three types of fuels such as solid fuels, example, wood, coal, peat, anthracite, etc. Second one is the liquid fuels, example, petrol, diesel, crude oil, kerosene, etc. And the third one, gases fuel, example, natural gas, biogas, chemical gas, etc. So these are the three types of fuel. Now just we'll start our main point that is how these fuels are compared over each other. So this is the first comparative point known as ignition temperature and this comparative point we have to compare on solid, liquid and gases fuel. Before comparing we'll see what you mean by ignition temperature. So ignition temperature is the minimum temperature at which the fuel is required to heat so that fuel undergoes combustion continuously. And a good fuel is which possesses moderate ignition temperature because higher ignition temperature causes difficulty to maintain and lower ignition temperature causes accident. And therefore by knowing the meaning of ignition temperature now we'll see the comparison. The solid fuels have higher ignition temperature, liquid fuels have moderate ignition temperature and gases fuels have lower ignition temperature. This is the second comparative point known as calorific value. Before starting the comparison again we'll see what you mean by calorific value. Calorific value is the capacity of fuel to supply heat when a unit mass of fuel is burned completely. Solid fuel contains low levels of carbon, liquid fuel contains moderate levels of carbon and gases fuel contain more levels of carbon. Therefore solid fuels have low calorific value, liquid fuels have moderate calorific value and gases fuels have higher calorific value. A good fuel is a fuel which possesses higher calorific value. Now just we have learned the explanation what you mean by calorific value that we can correlate with the definition of fuel also because the amount of the heat that is evolved by burning any fuel it mainly depends upon what is the level of carbon present in that fuel. If the carbon is more automatically the heat will be more. If the carbon is moderate the heat is moderate. And therefore here by learning the meaning of calorific value we know that the solid fuel possesses lower calorific value, liquid fuel possesses moderate calorific value, gases fuel possesses higher calorific value. And finally we have learned that a good fuel is a fuel which is rich in the calorific value because the heat is directly used for different kinds of work and therefore we are expecting that a good fuel should possess more calorific value. Now this is the third comparative point that is moisture content and what do you mean by moisture content? We know that the source of all types of fuels is in nature therefore there is a more possibility of coming moisture inside the fuel sample. Only the solid possesses more moisture, liquid possesses moderate and gases are free from the moisture content. So what is moisture content? It means the amount of water present in a fuel. The origin of all types of fuel is in nature. Solid fuels are mainly obtained from the trees. Therefore solid fuel consists of more moisture, liquid fuel consists of moderate moisture and gases fuel is free from moisture content and a good fuel is a fuel which is free from moisture content because moisture content is again related with the calorific value. If the moisture content is more the calorific value is low and if the moisture content is nil the calorific value is higher and therefore if you apply this knowledge for comparison we will come to know that the solid fuels are more in moisture content liquid fuels are moderate in moisture content and gases fuels are free from moisture content. Here I would like to ask you one question. A good fuel is a fuel which possesses dash dash ignition temperature. Just now we have learned ignition temperature and the question is that a good fuel is a fuel which possesses dash dash ignition temperature option A higher, option B lower, option C moderate and option D none of these. Think for a moment we will come with answer and the correct answer is option C moderate ignition temperature because we have learned if the ignition temperature is higher it is difficult to maintain and create and if the ignition temperature is low the possibility of catching the fire is more and therefore a good fuel is a fuel which possesses moderate ignition temperature. Now this is the next comparative point that is velocity of combustion. Now what is velocity of combustion? It means the speed at which the fuel undergoes combustion as solid fuels are low in carbon and more in moisture content. It shows lower velocity of combustion. The fuel consists of moderate levels of carbon and moisture. Therefore its velocity of combustion is moderate. Gaseous fuels are rich in carbon and free from moisture therefore it shows higher velocity of combustion and a good fuel is a fuel which possesses moderate velocity of combustion which is easy to maintain and to control also. So what is velocity of combustion? The speed at which the fuel undergoes combustion and it mainly depends upon the percentage of carbon also and the amount of non-combustible matter also and by referring that the comparison is that the solid fuel have the lower velocity of combustion liquid fuel have the moderate velocity of combustion gaseous fuels have the higher velocity of combustion. This is one more comparative point that is products of combustion. Now why we have to learn the products of combustion? Because when any fuel undergoes combustion depending upon the type and amount of non-combustible matter it emits some byproducts into atmosphere, into environment and that is related with the environmental quality. Nowadays we are facing lot of issues with environment and one of the major reason for environmental issues is the combustion products. What is that explanation? The solid fuel is rich in non-combustible matter, moisture and volatile matter. Therefore on combustion of solid fuel it emits ash and hazardous gaseous emissions on large scale. Whereas liquid fuel consist of elements like sulphur, nitrogen, oxygen and hydrogen which on combustion emits the corresponding gases as a harmful emission. So we know that the vehicular emissions are reaching oxides of sulphur, oxides of nitrogen and that is nothing but the harmful products of combustion. Whereas gaseous fuels are free from non-combustible matter, moisture therefore it emits no combustion products and a good fuel is a fuel which does not emits any products on combustion. That's why nowadays we know that gaseous fuels are known as a clean source of energy because gases are free from non-combustible matter and impurity therefore it will not emit any kind of emission whereas solid emits more kinds of harmful products. This is also one of the comparative point that is storage and transportation. Solid fuel possesses higher ignition temperature therefore it will not catch fire easily and hence it can be stored or transported openly in atmosphere whereas liquid fuel possesses moderate ignition temperature therefore it may catch fire at lower or moderate temperature and hence it can be stored or transported through a closed system. Gaseous fuel possesses very low ignition temperature therefore it can be stored or transported through closed system under pressure. So it is mainly related with the safety and we know that solids have more ignition temperature therefore there is no possibility of catching the fire therefore it can be stored or transported openly. Liquid have moderate ignition temperature therefore it can be stored or transported close to atmosphere and gases are very low in ignition temperature therefore it can be stored or transported in a closed system under pressure. So all this I have referred by using a textbook of engineering chemistry written by Jain and Jain. Thank you.