Ever Wondered what happens if you fill the wrong fuel in the car?

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Have you ever been to the fuel station to refill your car and ended up filling the wrong fuel? Well, don't worry because you were not the only one who did this. Close to 1,50,000 people every year fill the wrong fuel in their cars and men do this twice as much. In a country like India, this mistake is generally caused after telling the fuel pump attendant how much fuel to fill but not the informing which fuel to fill. But have you ever wondered what happens if you drive after filling the wrong fuel in the car? 

Before knowing what happens to the car, you must first need to know the major differences between petrol and diesel engines. Although all engines work on the principle of combustion, the method of combustion is different for petrol and diesel engines. The fuel types are so different from each other and with very different chemical properties. Autoignition temperature is the minimum temperature required for the ignition of the fuel. The autoignition temperature for diesel is 210 °C and 280 °C for petrol. This is one of the main factor to have different methods of combustion. 

 

           Petrol Combustion Chamber                                             Diesel Combustion Chamber

Now moving to the engine designs, the basic structure is the same. Both diesel and petrol engines have the same overall design including the fuel injectors, air valves and combustion chambers in which the pistons move. The difference here is in the ignition of fuel inside the combustion chamber. In petrol engines as the first piston moves down, the fuel-air mixture enters the combustion chamber. This is the first piston stroke. The mixture is compressed in the second stroke when the piston comes back up and the sparkplug creates a spark that ignites the fuel mixture. This ignition drives the piston down again creating the third stroke and the combustion gases are pushed out of the chamber on the fourth stroke with the piston moving up. 

Whereas in diesel engines, there is no sparkplug to create the ignition. On the first stroke, only air is let into the combustion chamber and on the second stroke the air is compressed to a pressure which is much more compared to that of  a petrol engine. This high pressure can increase the temperature of the air to 540°C. At this high-temperature diesel is injected and the fuel immediately ignites. The third and fourth strokes of the engine are the same as petrol engines.

Even though diesel has a lower autoignition temperature, the combustible property of diesel is lesser than petrol, hence diesel engines generally run at a much higher temperature.

So with two very different combustion processes, what happens if you fill the wrong fuel? Say diesel is pumped into a petrol fueled car. Diesel fuel is thicker and denser than petrol, the petrol fuel pump will struggle to move the diesel and petrol mixture through the engine. Also, the diesel will not be able to easily pass through the fuel filter. Instead, it will clog up the fuel filter. Whatever amount of diesel that then makes its way to the engine will clog the fuel injectors, making them inoperable. This will result in the engine gumming up and seizing. The petrol engine may run for a little while after diesel has been filled in the tank, but that is only because it is still running on the petrol leftover in the fuel line. Pouring petrol into a diesel tank would be far worse because of petrol's high combustion property, it would ignite much sooner than diesel fuel would. This early ignition and volatility could cause catastrophic damage to the diesel engine and its components.

The first thing to remember when you fill the wrong fuel is to not start the engine at any cost. This way the fuel will not move into the engine and will remain in that tank. Removing and cleaning the fuel tank is a much easier and cost-effective process. If the fuel starts running through the engine, damage of multiple parts like fuel injectors and pump is possible and it definitely will not be a cheap repair.

So next time watch out and fill in the right fuel ;)