s SCHOOL OF COMPUTING, ENGINEERING AND MATHEMATICS SEMESTER EXAMINATIONS 014/015 ME110 Aircraft and Automotive Systems Time allowed: ONE hour THIRTY minutes Answer TWO questions from THREE Items permitted: Any approved calculator Items supplied: Graph paper Marks for whole and part questions are indicated in brackets ( ) ME110_SEM_014/015 Page 1 of 6 Printing date: 3/09/015
Question 1 (a) The Tesla Model S electric vehicle can be bought with a battery pack having an energy capacity of 85 kwh. (i) The vehicle can be driven until the energy stored in the battery pack falls to 0% of capacity. Calculate the energy that has been used in kilo Joules (kj). (ii) During a journey through an urban environment the average power demanded by the motors is 7.9 kw, and the average energy conversion efficiency is 80%. Calculate the journey time (in minutes) if the energy stored in the battery pack falls from 70% at the start of the journey to 60% of capacity at the end of the journey. (iii) In preparation for an inter-city journey of 350 km the vehicle s battery is fully charged. If the vehicle travels at an average speed of 110 km/h the energy is consumed at a rate of 1 kw with an energy conversion efficiency of 85%. Determine whether the vehicle can complete the journey. (b) As an alternative to the Tesla Model S a driver selects a BMW 535d. This has a Diesel engine capable of producing 30 kw and a fuel tank with a capacity of 70 litres. (i) In urban driving conditions, the BMW consumes fuel at the rate of 6. litres per 100 km travelled. Calculate the mass of fuel consumed on a journey of 30 minutes at an average speed of 37 km/h. The density of Diesel fuel is 0.845 /litre. (4 marks) (ii) The Tesla completes the same journey having used 5% of its battery capacity. Based upon the energy stored in the vehicle determine which vehicle (BMW or Tesla) completed the journey in the most energy efficient manner. Assume that the lower heating value is 4.5 MJ/ and a higher heating value is 45.9 MJ/k for Diesel fuel. (6 marks) ME110_SEM_014/015 Page of 6 Printing date: 3/09/015
Question A pressure-volume diagram for a reciprocating internal combustion engine is shown in Figure Q (located at the end of the paper). (a) (i) Draw a sketch of a pressure-volume diagram for a -stroke engine. (ii) Draw a sketch of a pressure-volume diagram for a 4-stroke engine. (iii) Using Figure Q identify whether the engine is operating on a -stroke, or 4-stroke cycle. (1 marks) (b) Using Figure Q mark where the following events start and end: (c) (i) Induction of air into the engine (ii) Compression of the air (iii) Combustion of the air-fuel mixture (iv) Work is produced by the engine (v) The products of combustion are removed from the engine. At the start of the compression stroke: V = 0.44 litre, p = 78.5 kpa, T = 304 K At the end of the compression stroke: V = 0.04 litre (i) Find the compression ratio of the engine. (ii) Calculate the pressure and temperature of the air at the end of the compression stoke, assuming that the air behaves as an ideal gas. (1 mark) (3 marks) Question continues over the page ME110_SEM_014/015 Page 3 of 6 Printing date: 3/09/015
Question continued (iii) When Figure Q was recorded the engine was running at a speed of 500 rev/min and consumed fuel at the rate of 1.99 /h per cylinder. What was the air to fuel ratio? (iv) Assuming that there is no change in volume during the combustion process, calculate the temperature at the end of the combustion process. Useful equations For an ideal gas During compression Conservation of energy Constants R = 0.87 kj/ K cv = 0.718 kj/ K n = 1.35 pv mrt n pv constant Q pdv mcvt (4 marks) Gasoline fuel has a lower heating value of 4.7 MJ/ and a higher heating value of 46.7 MJ/. ME110_SEM_014/015 Page 4 of 6 Printing date: 3/09/015
Question 3 (a) A simplified equation for the combustion of a hydrocarbon in air is given by equation 3.1. This assumes that the air is a mixture of nitrogen and oxygen. C H a b where (i) (ii) nn n m mo 3.76 aco 1 bh O nn... 3.1 Gasoline is a mixture of hydrocarbons with a=8 and b=16. Calculate the number of moles of oxygen molecules, m, required for complete combustion. (4 marks) For the reaction given in equation 3.1 calculate the air to fuel ratio for gasoline. Take the molar masses to be as follows: M H 1 M kmol C 1 M kmol N 14 M kmol O 16 kmol (6 marks) (b) The conservation of energy equation for a closed system (i.e. one with a constant mass) is given in equation 3.. dp p dv dq 1... 3. d V d V d (i) (ii) (iii) List the parts of a four stroke engine cycle can be modelled by equation 3.. What type of energy transfers do the terms on the right hand side of equation 3. represent? Derive an equation for the rate of heat release with respect to crank angle during combustion that can be substituted into equation 3. to model the combustion process in an ideal Diesel cycle. (6 marks) (c) Newton s law of cooling may be stated as follows: dq has T wall T dt where h is the convection heat transfer coeeficien t kw / m K A is the surface area m s... 3.3 Derive an equation for rate of wall heat transfer with respect to crank angle for an engine with a cylinder bore of b and a rotational speed of N. ME110_SEM_014/015 Page 5 of 6 Printing date: 3/09/015
Student Number Figure Q ME110_SEM_014/015 Page 6 of 6 Printing date: 3/09/015