 I am Dr. Prakash Sarunke, Associate Professor from Department of Mechanical Engine, Vulture Institute of Technology, Solapur. Today we shall be discussing requirements of fuel system in CI engine as a continuation in our IC engine series. At the end of this session, students will be able to explain the fuel supply requirements for CI engines. Students will also describe air injection system. Introduction to fuel injection system. Fuel injection system is important component in CI engine. CI means compression ignition engine, where fuel is injected inside the cylinder. When fuel is injected into the combustion chamber, it is atomized. When fuel is injected, it is atomized. Atomization means what? What do you understand by the term atomized? Yes, can anybody tell? Think over it. Atomization means breaking of fuel into very fine droplets. Very fine particles, particles. These droplets vaporize due to heat transfer from the compressed air and form a fuel-air mixture. So for vaporization purpose, atomization is necessary. Due to continuous heat transfer from hot air to the fuel, the temperature reaches a value higher than the self-ignition temperature, self-ignition temperature of the fuel. Because the air is compressed, so it is hot and so it will be transferring heat to the fuel. Now what are the requirements of fuel injection system? So this causes the fuel to ignite spontaneously initiating the combustion process. When self-ignition temperature is achieved, attained, then say the fuel will ignite automatically because it has already reached its ignition temperature. For better performance of engine, following requirements are there. Timing and period of injection should be precise because power and economy both have to be ensured. And for that say these two factors are important. Secondly, amount of fuel injected must be accurately metered. That means measured so that you can achieve the economy and ensure what is required quantity say that only will be injected. Quantity should meet changing speed and load requirements. Especially in at ovals we know that speed load both go on changing. So the quantity should vary according to the need of speed and load for higher speed and higher load. So we need more quantity so it should be adjusted accordingly. Further, rate of injection should result in the desired heat release pattern. So heat release pattern should be desired as per the expectation depending upon the same need of that particular type. So heat release pattern we shall be discussing again in this detail in combustion. Then say atomization of fuel we have seen that unless say it is broken in the fine droplets it will be very difficult to vaporize it and mix it with the air particles so atomization is one more requirement. Spray pattern should ensure rapid mixing of fuel and air. The spray pattern the way in which the fuel will be sprayed so that should ensure rapid mixing of fuel and air. In uniform distribution of fuel droplets in the combustion chamber. So there should be uniform distribution throughout the combustion chamber. Beginning and end of injection should be sharp to eliminate dribbling of fuel droplets into the cylinder. So this is one more thing. So both should be sharp otherwise if they are taking some time they will be dribbling means leakage of fuel droplets into the cylinder. Now if there is dribbling say then there will be problems of any I mean carbon deposition and all this thing. To ensure uniform distribution of mutated fuel to all cylinder in case of multi cylinder engines. Especially in multi cylinder engines say uniform distribution to meet all cylinders. It should not happen that the cylinder which is closer it will get more and which is further so that will get less like that. Then weight and size of fuel injection system should be minimum. So this is naturally expected because it will be carried on the engine so that is there and ease of repair economic so that is always there for any equipment as such. But particularly say for fuel injection system so that is essential. Then what are the elements of fuel injection system? To accomplish these requirements following functional elements are normally required in a fuel injection system. Pumping elements to transfer fuel from fuel tank to cylinder. Metering elements to measure and supply the fuel according to varying speed and loads. Timing controls to adjust the rate of metering of fuel. Then distributing elements to divide the metered fuel quantity uniformly among the cylinders say distribution. So uniform distribution and different especially in case of multi cylinder engines. Timing controls for starting and stopping the injection accurately. So we have seen that sharp timing should be there and quantity should be metered. So for that timing controls are required. Then mixing elements for atomizing and distributing the fuel with air in the combustion chamber. So better mixing will ensure better combustion and for that mixing must be I mean better. Then various designs of fuel injection systems are available that we shall be I mean discussing now. See fuel injection systems are classified as air injection system and solid injection system. Let us discuss them first air injection system. Air injection system fuel is forced into the cylinder by means of compressed air. So compressed air is used say which will be I mean forcing the fuel so it will mix with the fuel and it will force the fuel inside the cylinder figure shows the schematic layout of typical air injection system. So let us see the figure yes. Now you can see here so this is the multi stage air compressor to raise the pressure of the compressed air I mean air. Then it will be going to different cylinders for this line and here there is this is cylinder so air will be coming from here and here there is metering pump. So fuel will be transferred first from transfer pump low pressure pump will be there. So it will supply it here to metering pump then metering pump will further enhance the pressure and high pressure fuel will come here and air will now mix with this fuel and it will force the fuel inside the cylinder. So this is for cylinder 1, cylinder 2 and all these metering pumps so their control is done with the help of camshaft. So these are the mechanical linkages say which are I mean coupled here and say they will adjust the timing okay. So this is how air injection system works. Now the fuel is metered and pumped to the fuel wall by a fuel pump which is driven by a camshaft so that we have seen just now so this is also called sometimes as high pressure pump. A multi stage air compressor supplies air to fuel wall at a pressure of around 60 bar to 70 bar. So that is the pressure range. So this is I mean high so we require multi stage air compressor. Fuel wall is opened through a mechanical linkage by camshaft. So we have seen that mechanical linkage is operated with the help of camshaft. The blast of air shifts the fuel along with it and is spread inside the combustion chamber in a well atomized form. So that is there so mixing will be there also and atomization will also be there. So let us see merits and demerits of air injection system. One advantage is good mixing of fuel with the air with resultant higher mean effect to pressure. Another is the ability to utilize the fuel of high viscosity which are less expensive than those used by the engines with solid injection system. This system is not used much nowadays because it requires a bulky multi air stage compressor and it is not possible to carry on the vehicle. This also increases engine weight and reduces the brake power output. So for this discussion we have taken the references from IC engines. So that is a book by ML Mathur and RP Sharma, Dhanpat republications. Fuel combustion engines, book by V Ganeshan, McGraw Hill Education India, so that is the publisher. I thank to them and I thank you also for patient listening.