The topic of Petrol vs Diesel Cars is indeed a very dilemma inducing one that most of us go through before purchasing a car. Previously, we covered an article comparing the running costs of both so that you can make a more informed decision. Here we will compare the different properties of both. We will also take a look at the reasons behind what makes their respective fuels display these vastly different properties despite being used to achieve the same purpose. So let’s get started with Petrol vs Diesel Cars: United by Use, Divided by Utility.
The ignition process denotes how the fuel starts burning once it’s inside the engine. The ignition process used in a petrol car is called spark ignition. In this process, a pre-mixed air-fuel mixture is ignited using a device known as a spark plug. The spark plug is used to generate a very small electric spark once the mixture is inside the combustion chamber. When this spark comes into contact with the air-fuel mixture, it catches fire and starts the combustion.
A diesel car, on the other hand, is devoid of a spark plug and uses a process called compression ignition. Here, only air is present in the combustion chamber initially. This air is strongly compressed by the piston which causes it to become very hot. The fuel is then directly sprayed into this hot air which causes it to simultaneously catch fire.
Now here you may wonder why diesel engines follow such a complex procedure instead of just using a simple spark plug. This is done because diesel has a much higher ignition temperature than petrol (56°C vs -44°C). Hence diesel won’t catch fire by simply introducing it to a tiny spark. It requires the help of a strong compression force to help it do the same.
It is a well-established fact that short stroke engines can operate at high peak RPM’s and are good for power while long stroke engines operate at low peak RPM’s and produce higher torque. Stroke length is simply the distance travelled by the piston from the lowest point to the highest point. A petrol engine has a shorter stroke which allows it to be revved more and put out more power. A diesel engine, on the other hand, has a longer stroke since it needs more compression to burn. This makes it rev less but put out a lot of torque for the same engine size.
In daily usage, this translates to better city usability for the petrol car. Since you have a much wider RPM range to explore, it gives you a freedom factor to tackle different situations like slow traffic, open roads or even a pinch of highways in a balanced manner. A diesel car is best suited for the highway where the waterfall of torque allows you to comfortably cruise at decent speeds without having to rev the nuts out of the engine. Another added bonus is that the high torque will make overtaking manoeuvres a breeze.
The NVH (Noise, Vibration and Harshness) factors are drastically different for both cars. A petrol car is always more refined, less noisy and smoother to drive in comparison to a diesel car. This is because the combustion process is more streamlined and controlled inside a petrol engine. The fuel and air in the case of a petrol engine are pre-mixed and released into the combustion chamber in a very precisely calculated quantity. This leads to a much quieter engine operation and a more refined driving experience in a petrol car.
In the case of a diesel car, the fuel and air are released separately resulting in a non-uniform air-fuel mixture.The combustion process, in this case, is very instantaneous and violent as the fuel begins to burn the moment it comes in contact with the hot air. This spontaneous process is the cause of the vibrations and excess noise coming from the engine. Another contributing factor to this attribute is the fact that they follow a long stroke cycle and hence deal with stronger forces inside.
As for pollution levels, diesel engines discharge a higher quantity of overall pollution. Although they generate lesser amounts of conventional pollutants than petrol (CO2 and CO), they generate exponentially higher quantities of NO2 and SPM (Suspended Particulate Matter). This is caused due to their heterogeneous nature that leads to a somewhat inefficient combustion process.
A petrol engine is usually cheaper to manufacture in comparison to a diesel engine. However, petrol as a fuel is significantly more expensive than diesel. A diesel engine is more expensive to manufacture than a petrol engine. This is because a diesel engine is exposed to much more extreme conditions like high pressure, higher compression ratio and higher temperatures due to the fuel’s properties. Hence the parts used inside a diesel engine are required to be stronger in nature to withstand these forces. This increases their manufacturing cost. Diesel as a fuel although, is cheaper than petrol.
Coming to maintenance factors, diesel engine parts are usually longer lasting as they are built much tougher than petrol engine parts. But when they do require replacement, they will certainly be more expensive to replace. Petrol engine parts don’t need the extra toughening and hence cost lesser. The same lack of toughening also implies that petrol engine parts will experience more wear and tear compared to diesel engine parts and will require sooner replacement.
Click here to see our detailed ownership cost analysis of petrol vs diesel cars.
Despite the fact that we have discussed so many points, we still have to conclude that there is no sure shot winner between these two. The boons of a petrol car can only be highlighted if they are mostly used for short-distance regular city rides. Vice-Versa, a diesel will simply shine in long-distance constant highway runs. At the end of the day, it pretty much boils down your preference and the conditions you will be using your car in. But going by the holistic overview, this battle ends in a stalemate.