Question 7 (10 Points): A turbojet engine operates with a net thrust of F_(n)=5000N and consumes dot (m)_(f)=0.4kg/s of fuel. Calculate the specific fuel consumption (cj) in kg/N.s Question 8 (10 Points): What is the difference between a turbojet, turbofan,and ramjet engine in terms of and propulsive efficiency, themaleficiency and specific file consumption

Question 7:<br />The specific fuel consumption (SFC) is a measure of the efficiency of an engine, defined as the amount of fuel consumed per unit of thrust produced. It is typically expressed in units of mass per unit of thrust per unit of time, such as kg/N.s.<br /><br />To calculate the specific fuel consumption for the turbojet engine, we can use the following formula:<br /><br />SFC = (dot{m}_f) / (F_n)<br /><br />where:<br />- SFC is the specific fuel consumption (kg/N.s)<br />- dot{m}_f is the fuel consumption rate (kg/s)<br />- F_n is the net thrust (N)<br /><br />Given:<br />- F_n = 5000 N<br />- dot{m}_f = 0.4 kg/s<br /><br />Substituting the values, we get:<br /><br />SFC = (0.4 kg/s) / (5000 N) = 0.00008 kg/N.s<br /><br />Therefore, the specific fuel consumption of the turbojet engine is 0.00008 kg/N.s.<br /><br />Question 8:<br />The main differences between a turbojet, turbofan, and ramjet engine in terms of propulsive efficiency, thermal efficiency, and specific fuel consumption are as follows:<br /><br />1. Propulsive Efficiency:<br /> - Turbojet: Turbojets have the highest propulsive efficiency among the three engines, as they are designed to operate at high speeds and generate a significant amount of thrust.<br /> - Turbofan: Turbofans have a lower propulsive efficiency compared to turbojets, as they are designed to operate at lower speeds and generate less thrust.<br /> - Ramjet: Ramjets have the lowest propulsive efficiency, as they are designed to operate at very high speeds and rely on the ram effect to generate thrust.<br /><br />2. Thermal Efficiency:<br /> - Turbojet: Turbojets have the highest thermal efficiency among the three engines, as they are designed to operate at high temperatures and pressures, which allows for more efficient combustion and energy conversion.<br /> - Turbofan: Turbofans have a lower thermal efficiency compared to turbojets, as they operate at lower temperatures and pressures.<br /> - Ramjet: Ramjets have the lowest thermal efficiency, as they operate at lower temperatures and pressures, and the combustion process is less efficient.<br /><br />3. Specific Fuel Consumption:<br /> - Turbojet: Turbojets generally have the lowest specific fuel consumption among the three engines, as they are designed for high-speed, high-thrust applications and can achieve a high thermal efficiency.<br /> - Turbofan: Turbofans have a higher specific fuel consumption compared to turbojets, as they are designed for lower-speed, lower-thrust applications and have a lower thermal efficiency.<br /> - Ramjet: Ramjets have the highest specific fuel consumption among the three engines, as they are designed for very high-speed, low-thrust applications and have a low thermal efficiency.<br /><br />In summary, turbojets have the highest propulsive efficiency, thermal efficiency, and lowest specific fuel consumption, while ramjets have the lowest propulsive efficiency, thermal efficiency, and highest specific fuel consumption. Turbofans fall in between the two, with a lower propulsive efficiency, thermal efficiency, and higher specific fuel consumption compared to turbojets.