--- title: "Diesel plant lubrication and cooling systems" subject: "Power Plant Equipment" chapter: 5 key: "semester_7/power_plant_equipment:diesel-lubrication-cooling" source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/diesel-lubrication-cooling site: BCT Engineering --- # Diesel plant lubrication and cooling systems Power Plant Equipment · Chapter 5: Diesel Power Plant - Asked in: 2081 Bhadra, 3+5 marks; 2080 Bhadra, 8 marks (asked 2 times) - Video: [Lubrication systems in diesel engine powerplant | mechanical lectures | mechanical engineering](https://www.youtube.com/watch?v=BJnD5NgHCn0) — Mech Surge - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/diesel-lubrication-cooling - Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-5 ## Question Why do we need lubricating system in a Diesel Power Plant? Describe cooling systems commonly used for cooling diesel power plant with the neat sketch. ## Short answer Lubrication reduces friction and wear, carries heat, seals piston rings, cleans contaminants, and prevents corrosion. Common cooling systems are open once-through, closed recirculating with heat exchanger or cooling tower, and air cooling for small engines. ## Answer #### Need of lubricating system Lubrication puts a thin oil film between moving surfaces of the engine. It is needed to: - reduce friction and wear between piston, rings, liners, bearings and gears; - carry away heat from pistons and bearings (cooling action); - seal the gap between piston rings and liner, so compression and power are not lost; - clean the parts by carrying away carbon and metal particles to the filter; - prevent corrosion and reduce noise. Without lubrication the parts would overheat and seize in a few minutes. #### Cooling systems of a diesel power plant About 25–35 % of fuel heat goes to the cylinder walls. If not removed, the lubricating oil breaks down, pistons seize and valves warp. The main methods are given below. **1. Open (once-through) cooling system** ```text River/well -> pump -> filter -> engine jacket | river (downstream) <-----+ hot water ``` Water is taken from a natural source, passed through the jacket once and discharged. Simple and cheap, but needs plenty of clean water; scaling from impurities. **2. Closed (recirculating) cooling system** - used in most plants. ```text +-> engine jacket -> hot water -> heat exchanger -+ | (soft water) | +---- pump <---- expansion tank <-----------------+ raw water side: cooling tower/pond -> pump -> HX -> tower (spray) ``` Soft (treated) water circulates in a closed loop through the engine jacket and a heat exchanger. The heat exchanger is cooled by raw water from a cooling tower or spray pond (or by air in a radiator for small sets). No scaling in the jacket, little water loss, so it is preferred. **3. Air cooling** (small engines only): fins on the cylinder and a fan blow air over them. Simple, but cooling is not uniform and suits only small sets. | Feature | Open system | Closed system | |---|---|---| | Water need | Large, continuous | Small make-up | | Scaling | Yes | Very little (soft water) | | Cost | Low | Higher | | Use | Where water is plentiful | Most diesel plants | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is NOT a purpose of the lubricating system? A. Reduce friction and wear B. Carry away heat from pistons and bearings C. Seal the piston ring to liner gap D. Increase the engine's fuel injection pressure Answer: D. Lubrication reduces friction, cools, seals and cleans; injection pressure is produced by the fuel injection pump. (Key point: Purposes of lubrication) 2. What happens if heat going to the cylinder walls (25-35% of fuel heat) is not removed? A. Efficiency rises B. Lubricating oil breaks down, pistons seize and valves warp C. Fuel injection is faster D. Nothing, the exhaust carries it all Answer: B. Excess temperature destroys the oil film and causes seizure and thermal distortion. (Key point: Why cooling is required) 3. How does the closed (recirculating) system work? A. Raw river water passes once through the jacket B. Soft water circulates through the jacket and a heat exchanger cooled by raw water from a tower or pond C. Air blows over fins only D. Fuel is used as coolant Answer: B. Treated soft water stays in a closed loop, so there is no scaling in the jacket and little loss. (Key point: Closed cooling system) 4. Compared to the closed system, the open (once-through) system has: A. Small make-up water need and no scaling B. Large continuous water need and scaling from impurities C. Higher cost and better temperature control D. A heat exchanger Answer: B. The open system is cheap and simple but needs plenty of clean water and scales up. 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