Diesel noise, vibration reduction and cooling

Diesel engines produce high noise (from combustion knock, air intake, exhaust and mechanical parts) and vibration (from unbalanced reciprocating masses and fluctuating torque). Both must be controlled for the safety of the plant, operators and neighbours.

Methods to reduce noise

1. Exhaust silencers (mufflers): reactive (chambers and baffles) and absorptive types reduce exhaust noise, the biggest source.
2. Intake silencers / air filters on the air intake to damp suction noise.
3. Acoustic enclosures and canopies lined with sound-absorbing material (mineral wool, foam) around the engine–alternator set.
4. Sound-insulated engine house: thick masonry walls, double doors, acoustic louvres for ventilation air.
5. Locating the plant away from residential areas; exhaust stack pointing upward, away from buildings.
6. Good combustion (correct injection timing, quality fuel) to reduce diesel knock.
7. Proper maintenance: tight joints, balanced fans, lubricated gears.

Methods to reduce vibration

1. Heavy concrete foundation (mass several times engine weight) isolated from the building floor by an air gap or sand.
2. Anti-vibration mounts: springs, rubber pads or cork placed between engine skid and foundation.
3. Balancing of rotating and reciprocating masses; multi-cylinder engines with suitable firing order; balance weights on the crankshaft.
4. Flywheel to smooth torque fluctuation; vibration dampers on the crankshaft for torsional vibration.
5. Flexible connections (bellows, flexible hoses) in exhaust, fuel and water pipes so vibration is not carried to the building.
6. Proper alignment of engine and alternator shafts; flexible couplings.

Cooling system of a diesel power plant

About 25–35 % of the fuel heat flows to the cylinder walls, head, valves and pistons. The cooling system removes it to prevent overheating, thermal stresses, distortion and breakdown of the lube-oil film, while keeping the engine warm enough for good combustion.

Methods: air cooling (small engines, fins and fan) and water cooling (all power-plant engines): open once-through, thermosiphon, forced circulation and closed (double-circuit) systems.

Closed forced-circulation system (common in power plants):

 ENGINE jackets --> Heat exchanger --> Pump --+
      ^          (soft water loop)            |
      +---------------------------------------+
                     |   ^
          hot raw    v   |  cold raw water
              Cooling tower / spray pond

1. A pump circulates soft (treated) water through the cylinder jackets and heads; water leaves at about 70–85 °C.
2. In the heat exchanger, raw water takes this heat; the soft water returns to the engine.
3. The raw water is cooled in a cooling tower or spray pond and reused.
4. A thermostat bypasses the cooler during warm-up; an expansion tank allows for volume change and make-up.
5. Lube-oil coolers are placed in the raw-water circuit.

Soft water in the closed loop prevents scale and corrosion; the raw-water loop with a cooling tower reduces water consumption.