The following relation is used to calculate the thermal effi

The following relation is used to calculate the thermal efficiency () of a natural-gas internal combustion engine:

= P/(m_f.HV)

Here, P is the power output in kW, m_f is the natural-gas mass flow rate in kg/s and HV is the heating value f the natural gas in kJ/kg. To establish the mean (nominal) value for the efficiency of the engines from a production batch, five engines were tested under similar conditions, and the following results were obtained:

Efficiency 31.0, 30.5, 30.8, 30.6, 30.2

The average values of P, m_f, and HV are 50kW, 0.2 kg/minute, and 49,180 kJ/kg, respectively. The systematic uncertainties have been evaluated at 0.2 kW, 0.003 kg/minute, and 1500 kJ/kg, respectively. Calculate the mean value and the uncertainty of the efficiency of this production batch for a 95% confidence level.

Solution