[sheets you give I. Describe briefly the losses associated to the blowdown, the pumping and the blowby phenomenon in an internal combustion engine. Explain briefly bow these losses can be controlled II. Give some examples of fuels used for powering SI and Cl combustion engines. Explain what do you understand by fuel self ignition phenomenon? Which fuel parameters are introduced to qualify a fuel in Sl and Cl engines? III. Consider a four-stroke combustion engine working on a Dual cycle with a compression ratio ry of 9 and a cut-off ratio re of 1.8. This engine has a cylinder bore B of 250 mm and a stroke length of 400 mm. For the cycle, it is assumed that the heat added at constant volume is half of the heat added at constant pressure, and the processes of compression and expansion follow a polytropic process defined by the law: P.V" constant, where P is the pressure, V is the volume and n is an exponent equal to 1.25). The initial state for induced air in the cycle are P1-1 bar and T1-30 °C for pressure and temperature, respectively. The used fuel has a heating value Qy of 40 MJ/kg. The working fluid is air with Cp of 1005 I/Kg K and Cy of 718 J/kg.K. 1. Sketch in the P-V and T-S diagrams the thermodynamic cycle. P V S 2. Determine the pressure and temperature at all salient points of the cycle. Give results as a table indicating values of pressures (bar) and temperatures (K) at each cycle state. 3. Show that the specific heat Qir exchanged in a polytropic process from initial state (0) to final state (f) is given by: Where: Y (C/Cy), T (gas constant), T, (initial temperature) and Tr (final temperature). 4. Determine the specific heat exchanged in the processes mentioned in the following table: Compression Heat values (kJ/kg) Combustion Expansion Exhaust 5. Determine the indicated thermal efficiency. Compare indicatively result with the efficiency that would be obtained in case of isentropic compression and expansion. Thermal efficiency (Th):- Efficiency comparison: International University of Raba Aerospace Engineering School/Aero Combustion Engines First & last name Midterm exam (January 18, 2018, from 14:00 to 16:00 PM) This is and notes exam No Smartphone or other electronic media is pred Write the final rely there sheet, and solutions deals an extra shes. Put your name in all sheels you give 6. Assuming a ratio of 50 % between actual and theoretical indicated work of the cycle, a mechanical efficiency m of 85 % and a combustion efficiency The of 95 %, determine in case where the engine operates at 3 cycles per second the brake power Ph, the torque T, the BMEP and the bsfc. Give results as following table: Brake power (kW) Torque (Nm) BMEP (bar) bufe (gr/kWh) Cise briefly three reasons behind the difference between theoretical and actual indicated work. IV. A liquid-liquid fuel mixture consists of 90 % octane (CsHix) and 10 % alcohol (C2H5OH) by volume. Both fuel and air enter in the combustion chamber at 25 °C and 1 atm. A dry analysis of the combustion products indicates by volume 7% of CO2, 0.5 % of CO and 10.9 % of O₂ Determine: 1. The composition by mass of this mixture: % CyHi and % C₂H5OH: 2. The balanced reaction equation for complete combustion: 3. The fuel equivalence ratio. Conclude about amount of air used in this combustion, 4. The equation for calculation of the adiabatic flame temperature Tad Give an approximate value of Tad. Use tables given in appendix. of Rabat Aerospace Engineering School/Aero 4 Combustion Engines First & last names: Midterm exam (November 16, 2017) This is a closed notes exam No Smartphone or other electronic media is permitted Write the final results on these sheets, and solutions details on extra sheets. Put your name in all sheets you give. I. Consider a four-stroke combustion engine working on Otto air-standard cycle between upper and lower absolute temperatures limits Tmax and Tmin, respectively. 1. What are the assumptions made in this ideal cycle? 2. Sketch in the P-V and T-S diagrams the thermodynamic cycle: P T 3. Show that the compression ratio for the maximum work is given by: 20-1) 4. Prove that temperatures TC and TE. respectively, at the end of compression and the end of expansion are equal. Express these temperatures in terms of Tmin and Tmax. II. A five-cylinder SI engine of 3.5 liters operates on a four-stroke cycle at rotational speed N of 2500 rpm. At these conditions, the engine has an indicated mean effective pressure IMEP of 1429 kPa, a mechanical efficiency 1m of 62 %, a volumetric efficiency ny of 80 %, an air-fuel ratio AF of 15, and a combustion efficiency ne of 97 %. Ambient conditions are 1 bar for pressure Pa and 20 °C for temperature Ta. The used fuel has a heating value QF of 42 MJ/kg. Calculate: 1. Indicated work W; in J developed in each cylinder at each cycle 2. Brake mean effective pressure BMEP (bar) 3. Friction mean effective power FMEP (bar) 4. Brake power Pb (kW) 5. Torque T (Nm) Wi- .J BMEP bar FMEP bar Pb kW T Nm 6. Mass air flow rate ma in gr/sec ma -grisec 7. Mass fuel flow rate my in grisec my gr/sec. 8. Brake specific fuel consumption bsfc in gr/kWh bsfc=.. gr/kWh 9. Conversion efficiency nf Final Exam Group B2 Date: January 15, 2018 Duration: 2 hours Arduino Prototype Good Luck! As long as the pushbutton is pressed, set the servo motor to 90 degrees and turn off the LED, If the word "TURN is received using the serial communication feature, then set the servo motor to 180 degrees, turn off the LED and turn on the active buzzer. Otherwise, print Invalid Instruction!" on the serial monitor and set the prototype to its initial configuration. Regarding the active buzzer, the loop has to vary between 15 and 85, the sound has to be generated only once (a bip). If the button is released and no instruction is received through the serial interface, set the prototype to its initial configuration. Each time you set the servo motor to a given position, wait for Is before executing the next action. Print out the state of the pushbutton to the serial monitor. The initial configuration consists of turning on the LED and setting the servo motor to 0 degree. Also, in this case, the active buzzer is not enabled. Declare pins as constants. The wiring has to be performed as follows: LED Device Button Active buzzer Servo motor Arduino digital pin 5 12 3 7 4 pts) 1. Provide the list of the required hardware. 6.5 pts) 2. Establish the circuit's schematic. 8 pts) 3. Write a function to set the servo motor to the required position. The function should have only one argument which is the position of the servo motor. This function has to be used whenever you set the position of the servo motor. 5 pts) 4. Write a suitable sketch. 1