Diesel Vs Petrol Engines. Why are diesel engine more noisy and fuel efficient ?


Diesel vs Petrol, most pertinent and relevant today with ever increasing petrol prices, making Indian car buyers skew their new car buying decisions in favour of diesel cars. We would love if car experts could contribute towards this diesel Vs petrol debate.


I have Two Questions:

1). Why Diesel Engine Produce More Noise than petrol Engine?

2) Why Diesel Engine gives more mileage than petrol?

Diesel Vs Petrol Engines. Why are diesel engine more noisy and fuel efficient ?

Diesel engine noise is referred to as a Clatter or Knock. Higher noise levels in a diesel engine could be;

1) Combustion noise

2) Mechanical noise

Combustion Noise is due to rapid build up of pressure inside a diesel engine during combustion stroke. In a diesel engine, the fuel ignites spontaneously shortly after injection begins. During this ignition delay, the fuel is vaporizing and mixing with the air in the combustion chamber. Combustion causes a rapid heat release and a rapid rise of combustion chamber pressure. The rapid pressure rise is responsible for the "diesel knock or clatter" which is very audible.

Combustion Noise can be reduced by increasing the Cetane number of any diesel fuel. This in turn decreases the amount of knock by shortening the ignition delay time considerable. Indirect injection systems limit the pressure rise by throttling of the combustion gasses through the pre-chamber throat.  Advanced direct injection engines use pilot injection to start combustion off more slowly. Injection timing, rate of injection, compression ratio, turbo boost, etc all effect how much diesel clatter one hearsMechanical Noise could be because of pump noise, gear rattle as big diesel engines  require super strength front end drives, such gears often rattle. Loose fitting pistons which skirts against the cylinder wall also can cause diesel clatter.

Diesel engines are more fuel efficient than petrol engines because

Diesel engines work on much higher compression ratio which packs in that much more energy in the mixture resulting in much better thermodynamic efficiency. Thanks to higher compression ratio diesel engine can work on much leaner air fuel mixture thus adding to its fuel efficiency. Lower pumping loses as the throttle is always wide open.


Petrol vs Diesel, April 27 2016.

VISITOR                                                      Sir I’m confused between petrol and Diesel     


VISITOR                                                      My running is 5000 km per year               


AGENT                                                        Obviously only petrol  


VISITOR                                                      Ok...    


VISITOR                                                      But resale value of petrol is far less than Diesel              


VISITOR                                                      So         


AGENT                                                        Going forward its diesel which is not going to be so much in demand  


AGENT                                                        One can expect diesel prices to grow faster than petrol even in India  


AGENT                                                        In any case even today there are more discounts on diesel than petrol cars      


VISITOR                                                      Yae thats right 


AGENT                                                        IN any case because you are going to be driving so less the higher diesel entry cost does not justify its purchase for you               


VISITOR                                                      Is there any difference between mileage of hatch and sedan in petrol


AGENT                                                        mileage difference is basically dependent on engine size and yes car size also affects the mileage                                                                     


AGENT                                                        so would be the weight of the car etc  


VISITOR                                                      All the petrol cars are with 1.2 ltr engine            


VISITOR                                                      I have seen grand i10 swift elitei20 Chevrolet sail and Ford Figo             


VISITOR                                                      And all sedan version of these cars       


VISITOR                                                      The rest drive sail and i found engine very smooth       


AGENT                                                        Among your list my priority will be elite i20, Swift, Grand i10 only. Other cars will really hit you on resale and service                                


VISITOR                                                      Ok