Marine Engineering and Systems
Marine Engineering and Systems covers propulsion machinery, auxiliary systems, power balance and fuel consumption. GATE NM tests the diesel cycle, turbocharging, shaft power, SFOC, pumps, heat exchangers and the redundancy needed for safe operation.
Core rules
- Indicated power is the power developed in the cylinders; brake power is at the shaft. Mechanical efficiency η_m = BP/IP.
- Specific fuel consumption SFOC = fuel mass flow/power, usually g/kWh. Daily fuel = P × SFOC × 24/10⁶ tonnes when P is kW and SFOC is g/kWh.
- Turbocharging raises charge density; aftercooling lowers intake temperature and increases mass flow.
- Pump power P = ρgQH/η for a liquid; system curves and pump curves intersect at the operating point.
- Heat exchanger duty Q = m c_p ΔT; log-mean temperature difference is used for sizing.
- Auxiliary systems include fuel treatment, lubricating oil, cooling water, compressed air, steering gear and electrical generation; redundancy is required for essential services.
Worked example
A main engine develops 5000 kW at SFOC 190 g/kWh. Fuel per hour = 5000 × 190 = 950,000 g/h = 950 kg/h. Per day = 950 × 24 = 22,800 kg = 22.8 t/day. If the plant burns heavy fuel oil of density 0.98 t/m³, the daily volume is 22.8/0.98 ≈ 23.3 m³/day. This is a mass balance, so the density is only needed to convert to volume.
Traps
SFOC is per kWh, not per hour; mixing units gives a factor-of-1000 error. Brake power is not the same as indicated power. A pump operating far from its best efficiency point may cavitate or overheat. In heat exchangers, use the correct specific heat and mass flow, and do not ignore fouling margins. Essential systems need redundancy, but adding redundancy does not remove the need for a blackout recovery procedure.