 I am Dr. Prakash Saunke, working as Associate Professor in Department of Mechanical Engine, Walsh and Institute of Technology, Solapur. Today, we shall be discussing in our IC engine series, the fuel system CI engines second. First, we have discussed earlier. So, at the end of this session, the students will be able to describe the working of different fuel supply systems used in CI engines. One of the most commonly used is common rail fuel injection system. Sometimes, it is also known as common rail diesel injection system, CRDI. Figure shows the schematic diagram of common rail system. We shall be seeing the figure. What do you understand by the word common rail? Yes, can anybody guess, think, tell? Common rail, right? There is one common rail through which fuel is supplied to all the cylinders, all the cylinders. In case of individual pump, we have seen that separate, I mean pump is there here, there is not such case. Only one pump and common rail through which fuel will be supplied to all cylinders. So, in this system, a high pressure pump supplies fuel under high pressure to a fuel header or accumulator. So, that means common rail. Fuel header or accumulator, that means common rail. A pressure regulating valve maintains constant pressure in the accumulator. In this common rail or in the accumulator or header, a pressure regulating valve is there so that will maintain a constant pressure. High pressure pump is multi-cylinder pump. Hence, pumping action is spread over a long period, thus reducing noise and stress of driving mechanism. So, we shall discuss this point again in detail. So, let us see first the, I mean figure. Now here, so this is HP pump. So, first fuel pump, transfer pump will supply the fuel to HP pump, say from the fuel tank. Now, there's only one common pump and this is the header or it is also a common rail. It is also known as common rail. And say through which fuel will be supplied to different cylinders, say from different lines. Of course, here two cylinders are shown. So, here injector however is separate for each of the cylinder. And this injector is operated with the help of rocker arm and pressure rod. So, that particular mechanism. So, this is the hinge. So, at correct time for each cylinder, fuel will be injected inside. Pressurized fuel will be supplied here, header. So, it will be coming up to here. But inside the engine cylinder, say it will be injected through the injector and that timing will be controlled with the help of the camshaft and this rocker arm mechanism. Okay? So, same for different cylinders. Now, coming to this point, high pressure pump is multi-cylinder pump. Hence, pumping action is spread over a long period, thus reducing noise and stress in driving mechanism. In case of individual pump system, say individual pump operates for each cylinder separately. And because of which say there is jerk also and that each pump is acting instantaneously almost say for that. So, there will be more noise and more jerk. Here, since there is only one common pump for all cylinder, its operation can be spread over a time. And since it is a multi-cylinder pump for each cylinder, there will be a separate, you know, working stroke. So, that way we can have a smooth pumping action which is spread over a long period and thus reducing the noise and stress. Okay? For each cylinder, a separate metering and timing arrangement is provided that we have seen. Metering element is connected to injector nozzle fitted on each cylinder normally through a pushrod and rocker mechanism. So, we have seen that pushrod and rocker mechanism which is operated with the help of camshaft. The amount of fuel is controlled by varying a pushrod stroke. So, pushrod stroke length, so that can be varied with the help of cam and camshaft. And accordingly, amount of fuel can be controlled, okay? So, this is how metering and timing controls are done. In this system, supply pressure is independent of engine speed. So, this is one more advantage as such because since it is a multi-cylinder system, so whether speed increases or decreases that operation is spread over a period so it doesn't get affected. In case of individual pump, if the speed increases then the timing for each pump operation so that will be different and so that will change the supply pressure. So, that way this system tends towards self-governing. So, automatic because even if there is change in speed so it doesn't matter so automatically that supply pressure is gone. So, this system requires matching of different nozzles for uniform supply and timing. So, this is required because on different cylinders the different nozzles will be there and say in these nozzles there should be matching so that will be uniform supply to each of the cylinder. So, matching has to be done. Say the type, I mean the line, I mean stroke length, et cetera, so all this required to be matching. So, there is one more system which is known as distributor system. So, there is further modification of this common rail. So, figure shows a schematic diagram of a distributor system that we shall see later. In this system the pump which pressurizes the fuel also does the function of metering and timing. So, this is the point where it differs from the common rail. Common pump is there and metering and timing will be again governed by the same pump for different semi cylinders at one place. In case of common rail for each of the cylinder there is separate metering and injector system. Here metering and distribution so these are metering and timing so that is I mean controlled centrally. The fuel pump supplies the required amount of fuel after metering it to a rotating distributor at the correct time for supply to each cylinder. We shall see the figure so that we'll understand this. Yes. So, this is the low pressure fuel will be coming from transfer pump say to this high pressure pump. Now, high pressure pump will be supplying the pressurized fuel to the distributor. This is common to all the cylinder and this will does the metering and timing for each cylinder and accordingly each of the pressure lines so that will be sent the fuel at correct timing. Here, here, et cetera. So, that is how it is called as distributor system. Now, the number of injection strokes per cycle for the pump are equal to the number of cylinders. Injector strokes for if there are four cylinders then for each cycle say there'll be four strokes. If there are two cylinders, two strokes like that. So, that is there. Now, what are the advantages? Because of one metering element pump uniform distribution is automatically ensured. For all cylinders uniform distribution will be there because only one metering element is there. So, that will be measuring say I mean in correct fashion. The system is economical as cost of fuel injection system also reduces by almost 33% of that for individual pump system. There's only one pump, there's only one distributor. So, all that will save the cost. So, that cost saving is almost 33% as compared to individual pump system. Now, if we compare the different fuel injection systems you will find that, so these are the common, I mean different types of pump systems. Air injection, individual pump system, common system and distributor. And these are the different functions, parameters of comparison. So, these are all the types of solid injection. In metering in case of air injection say pump is doing it. Here individual again here pump is doing it. In common rail injection wall say there itself and here in case of distributor we have seen that pump itself. Timing is controlled with the help of fuel camp here. Here there is a pump camp. So, that is separate for each pump. Then fuel camp which is common for all this species. So, it is called as fuel camp. Okay. Then injection rate is governed by spray wall here. Here pump camp, here spray wall and here fuel camp. Atomization is done by spray wall, spray tip. So, here there is a very small tip so that we shall be seeing later, spray tip. Distribution here it is done by the spray wall. Here it is spray tip, spray tip, spray tip. So, that is how a comparative statement will say see that comparison. Now cost wise of course we have seen that this distributor is most economical, then common rail and then individual pump. Okay. Individual pump is more costly app of all. Of course unit injector is again costlier. So, both are almost same in the range. Now, references for this particular discussion were taken from the book of IC engine authors Mathur and Sharma, Dhanpatraya publications. Similarly, IC engines book by V. Ganeshan publisher McGraw-Hale Education India. I thank to them and I thank.