Diesel technologies have been in India for quiet a long time but still is quiet under rated. We think its a low thing to have. Lets find out about it
What is fuel?
To many, fuel is something that burns the pocket when he/she owns an automobile. But lets see what it does(in a bit of detail):
The cylinders inside the engine of a car takes in air. Then the air is compressed by moving the pistons(present in each cylinder) to the top(aka TDC - Top Dead Center).Then fuel is sent into the cylinder through fuel injectors and the fuel is ignited.
Diesels get the heat for explosion by compression of the air. Air when compressed produces heat. Diesels use this heat to ignite. Diesels dont have spark plugs. They have something called’GLOW PLUGS’ which help in heating up the engine when the engine is starting from a cold temperature.
Ignition makes the temperature of the air to rise(to about 2000 degrees Centigrade). The increment in the pressure forces the piston down and this does work(expressed in Newton Meters or Nm or Kilogram Force Meters(Kgm) or Ft Lbf Feet Pound Force- physics geeks rejoice!). This work is used to move the vehicle. This is known as TORQUE
When it comes to automobiles, more than Torque we are familiar with the term Power expressed in Bhp or KW. BHP stands for Brake Horespower and KW stands for Kilowatts.
AMONGST IDENTICALS, DIESEL ENGINES HAVE MORE TORQUE AND LESS POWER THAN PETROL ENGINES
Diesels have a higher energy density than petrol.
Density of energy in petrol= 132 * 10^6 Calories
Density of energy in diesel= 152 * 10^6 Calories
And yet diesel costs less than petrol! That is because diesel requires less refinement(to be produced from crude oil) than petrol.
Thus diesels have more torque in one explosion than petrol.
But they have a low power. This is because, power is derived from Torque.
Power= Torque* Engine RPM(at this torque) / 5252
Thus we see that Power= Torque when engine RPM is 5252 and Power becomes more than Torque when RPM increases.
But the diesel engines are heavy and thus usually cannot go more than 5252 RPM. Even if it does, the torque starts to reduce rapidly as the engine’s efficiency reduces and the diesel engine that goes to this high RPM would not be very reliable too.
DIESEL IS FOR TOP SPEED WHEN PETROL IS FOR ACCELERATION
Petrol usually does well coz it is lighter.Thats it! Diesel is more efficient!
Lets look at Octavia’s diesel and petrol variants:
PETROL:
ENGINE SIZE - 1984 CC
POWER - 111 BHP
TORQUE - 16.8
TOP SPEED - 185
FUEL EFFICIENCY - 8.1 / 12.8(CITY / HIGHWAY)
WEIGHT - 1235KG
DIESEL:
ENGINE SIZE - 1896(WITH TURBOCHARGING)
POWER - 90 BHP
TORQUE - 21.4 Kgm
Top Speed - 187
WEIGHT - 1330KG
FUEL EFFICIENCY - 12.7 / 18.9(CITY / HIGHWAY)
The diesel is marginally higher than the petrol. But look at the power. Diesel is low on power, yet manages the top whack of 187 KPH! But acceleration is better in Petrol.
THE PROBLEMS WITH DIESEL
I was all positive about the diesel. But why does’nt anyone else favour it? That is because there are a lot of problems with diesel.
The maintenance of diesel is high. Since diesel deals with more power(=more heat), the engine requires servicing at shorter intervals. A number of things require changing each time and thus adds to’COST OF OWNERSHIP’
The diesel technologies available in India are poor. They are polluting vehicles. The engines are coarse and dont grab the attention of driving lovers. But companies are willing to invest in bringing in latest diesel technologies to India. Skoda and Hyundai(Elantra CRDi) are on their plans probably. Skoda Octavia has the best diesel engines(I AM NOT TAKING THE MERCEDES’ INTO CONSIDERATION)
Diesel engines are noisy and vibrate. Even Hyundai’s accent CRDi is noisy. Through the years, engineers have been able to eliminate the vibrations though.
CONCLUSIONS
Diesel is more dense in energy than petrol.
Diesel has less acceleration but more top speed.
Diesel cars require more maintenance
Diesel is cheaper than petrol
Diesel cars of same top speed return more fuel efficiency than their petrol variants.