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ENGR5003 / Week 4
Week 4 Q1Exercise sheetCurrent spec2:212 min

ENGR5003 Week 4 workshop sheet Q1

Consider a petrol engine operating on the Otto cycle. The compression ratio is 5 and 1 litre of air is drawn into the engine at 300 K and 0.85 bar. The specific heat addition per cycle is 1000 kJ/kg.

Formulas you may need
  • Otto efficiency: ηth=1−1rvγ−1\eta_{th} = 1 - \dfrac{1}{r_v^{\gamma-1}} (on the formula sheet)
  • Isentropic: T2T1=rvγ−1\dfrac{T_2}{T_1} = r_v^{\gamma-1}, p2p1=rvγ\dfrac{p_2}{p_1} = r_v^{\gamma} (on the formula sheet)
  • Isochoric heat addition: qin=cv(T3−T2)q_{in} = c_v(T_3 - T_2), cv=Rgγ−1c_v = \dfrac{R_g}{\gamma - 1} (on the formula sheet)
  • Ideal gas: pV=mRgTpV = mR_gT; Gay-Lussac p/Tp/T = const at constant volume (on the formula sheet)
  1. (a)
    Determine the thermal efficiency of the cycle.
  2. (b)
    Determine the maximum temperature and pressure of the cycle.
  3. (c)
    What is the net work output of the cycle?