Basics of Mechanical Engineering


Gasoline and Diesel Engines: A comparative Study

Gasoline Engine:
  1. Because of relatively low compression ratio, as well as low explosive power inside cylinder, the gasoline engine construction is easier, light-weight and less noisy. On the contrary, due to high compression ratio, resulting in very powerful explosion, Diesel engine is heavier construction more complicated and is noisy.
  2. With same displacement volume, the maximum power output is higher in gasoline engine. On the other hand, the maximum amount of fuel injection is limited in diesel engine.
  3. Servicing and maintenance of the carburetor in gasoline engine are easier. On the other hand, the fuel pump and the injection nozzle are complicated and their servicing & repairs are also complicated. 
  4. Because of lower compression ratio, starting is easier in a gasoline engine and can be done by an ordinary starting motor and a battery. Compression ignition engine, on the other hand, needs much more powerful starting motor and battery systems.
  5. Gasoline engines being lighter are better suited for light automobiles, small pumps etc., although fuel consumption in diesel engines is lower. However Diesel engines are more used in buses, trucks, heavy vehicles, generators, large pumps etc.
  6. Gasoline engine 'idling' is smooth and less noisy than Diesel Engine.
Diesel Engine:
  1. Compression ratio is high, as well as, heat efficiency is higher (30-34% against 25-28% of gasoline engine), and hence fuel consumption is low. For example, in diesel 170-220 gm/hp-hour and in gasoline 220-330 gm/hp-hour.
  2. Diesel fuel is cheaper, as well as fuel consumption rate is less, as mentioned above. As such running of Diesel engine is more economic.
  3. Engine 'knocking' problem is less and therefore cylinder bore can be increased with no risk.
  4. Torque and engine, performance in all speeds remain uniform and smooth , because the fuel injection pump always works in the same system and same pressure. On the other than in gasoline engine, at high speeds, carburetor efficiency is slightly reduced, so the torque development is also reduced to some extent.
  5. Combustion in the combustion chamber happens very easily, as only high pressure fuel is injected and no electricity is required. Gasoline engine needs electric spark for combustion and as such there are chances of misses due to electrical problems.
  6. Combustibility range of fuel (diesel) in compression ignition engine is much higher and so, the engine runs smoothly at all speeds. On the other hand, gasoline fuel's combustibility is limited and as such 'misfire' occurs in gasoline engines.
  7. Diesel fuel is less toxic (less hazardous for health) than gasoline (petrol)

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