I85PREP
⌘ K
Egypt Engineering Consultant Mechanical study materials
Egypt Engineering Consultant Mechanical study resources

Egypt Engineering Consultant Mechanical: Mechanical Power Systems and Energy Conversion

Egypt Engineering Consultant Mechanical · Work through your exam, one topic at a time.

All guide sections

Mechanical Power Systems and Energy Conversion

What the exam tests

This domain covers engines, gas turbines, steam and compressed-air systems, pumps, fans and generator sets. The exam tests performance curves, part-load efficiency, derating, fuel consumption, and the choice between prime and standby equipment in Egyptian installations.

Core rules

  • Generator rating is usually kVA at a power factor, often 0.8. Real power kW = kVA × pf. Do not compare a kW load with a kVA rating directly.
  • Prime-rated gensets tolerate continuous variable load; standby-rated sets are limited-hours. Choose by duty, not by lowest price.
  • Engine output falls with altitude and ambient temperature. Apply the manufacturer’s derating, not a generic rule.
  • Fuel consumption is usually given in g/kWh at a stated load. Specific consumption rises sharply below about 50 % load.
  • Fans and centrifugal pumps follow the affinity laws: flow varies with speed, head with speed squared, power with speed cubed. Variable speed is the main part-load energy measure.
  • Compressors: check volumetric efficiency, intercooling, and specific power in kW per m³/min. Leaks raise specific power.
  • Steam and gas turbines: use enthalpy drop and isentropic efficiency; do not use Carnot efficiency for a real machine.

Worked example

A 500 kVA genset at 0.8 pf is 400 kW. At 70 % load it delivers 280 kW. At 210 g/kWh, fuel use is 280 × 210 / 1000 = 58.8 kg/h. With diesel density 0.84 kg/L, that is 70 L/h. At 40 % load the same set might consume 240 g/kWh, so fuel use is 160 × 240 / 1000 = 38.4 kg/h, but the fuel per useful kWh is worse. Part-load efficiency matters more than hourly litres.

Traps

Treating kVA as kW; using standby rating for continuous duty; ignoring altitude and temperature derating; applying affinity laws to systems with large static head; comparing fuel in L/h without load context; forgetting compressor leaks and dryer pressure drop.

Key points

  • kW = kVA × power factor; generator ratings are usually at 0.8 pf.
  • Prime and standby ratings are not interchangeable.
  • Fuel consumption in g/kWh rises at low load.
  • Affinity laws: flow, head and power follow speed, speed squared and speed cubed.
  • Manufacturer derating applies for altitude and ambient temperature.