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ENGR5003 / Week 4
Week 4 Q2Exercise sheetCurrent spec2:120 min

ENGR5003 Week 4 workshop sheet Q2

Consider a petrol engine and a Diesel engine. The petrol engine has a compression ratio of 8 and the diesel engine has a cut-off ratio of 4. Given that for both cycles, 0.8 litres of air is drawn into the engine at 0.7 bar and 280 K:

Formulas you may need
  • Otto efficiency: ηth=1−1rvγ−1\eta_{th} = 1 - \dfrac{1}{r_v^{\gamma-1}} (on the formula sheet)
  • Diesel efficiency: ηth=1−1rvγ−1[rcγ−1γ(rc−1)]\eta_{th} = 1 - \dfrac{1}{r_v^{\gamma-1}}\left[\dfrac{r_c^{\gamma} - 1}{\gamma(r_c - 1)}\right] (on the formula sheet)
  • ηth=1−qoutqin\eta_{th} = 1 - \dfrac{q_{out}}{q_{in}}, wnet=qin−qoutw_{net} = q_{in} - q_{out} (on the formula sheet)
  • Indicated work = net work - pumping work; MEP=WindicatedVsMEP = \dfrac{W_{indicated}}{V_s} (learn this, Lectures 10-11)
  1. (a)
    What is the compression ratio of the Diesel engine, given that both engines have the same thermal efficiency?
  2. (b)
    Given that the specific heat rejected per cycle is 350 kJ/kg, how much heat is added each cycle and what is the net work output?
  3. (c)
    If the specific pumping work is 100 kJ/kg and the swept volume is 0.7 litres, what is the indicated work and the mean effective pressure?