The pressure diagram shown in Figure 1 refers to a reciprocating piston engine. During the P sequence 1,2,3,4,5 the engine intake and exhaust valves are closed, and the cylinder is a closed system. The exhaust valve is open during the exhaust stroke (5 to 6). The intake valve is open from 7 to 1. The working fluid is air, which you can treat as a perfect gas: R=287 J/Kgk, c₂=1005 J/Kgk c=718 J/KgK. The processes are as follows: Data 1-2 Isentropic compression V+V, 2-3 Heat addition at constant volume. The heat transferred to the working fluid is Q23 = myQLHV where QLHvis 120 MJ/kg and my is the fuel burnt to generate the heat transfer. The mass of fuel burnt is given by my where the Air to Fuel Ratio (AFR) is 34 AFR 3-4 Isentropic expansion 4-5 Heat rejection at constant volume The pressure ps, which is also equal to P6, is always 1bar during the exhaust stroke. The pressure p which is also equal to p₁, varies according to the demand for work output from the engine. The temperature T₁ is always 285K. The work done by the piston on the air during the intake and exhaust strokes is W = Vs (Ps - P7) where Vs is the swept volume of the engine. This is the volume swept by the piston as it moves from its lowest position to its highest position. The volume V of the system when the piston is at its highest position is the clearance volume of the engine. Its compression ratio is then c = (V₁ + Vc)/Ve Compression ratio Swept volume Air/fuel ratio Lower heat value of fuel Intake temperature 17. V/₂ AFR QLAY T₁ Fig 1 10 1x 10³ m³ 34 120MJ/kg 285K Calculations Give details of your calculations for each part in your report and underline your answers. For values of P1 of 1 bar (throttle fully open) and 0.3 bar (small throttle opening) calculate: a) The mass of trapped air (m₂) [10] [50] b) Pressures and temperatures at points 2,3,4 and 5 c) The net work output, Wet, (account for the work done during the intake and exhaust strokes in this) and the thermal efficiency calculated as net work output divided by heat supplied (Wnet/Q23). [25] Compare thermal efficiency for the two cases: throttle fully open and small throttle opening. Explain why the values are different. [15]

Fig: 1