So far we have discussed a lot about generators and their types, their uses, the basic working principle behind the operation of a generator, how to maintain your generator & many other aspects. In this article, we will discuss their fuel types- specifically two types; Diesel and Gasoline and analyse whether it’s better to own a diesel powered generator or a Gasoline(Petrol) powered one.
Before we even start discussing the pros & cons of each type of generator (diesel and petrol/gasoline) we have to understand a few key things first, which is really a part of basic Engineering and Engine Mechanics. Sounds complicated? Well, let us try to break it down into segments.
Firstly, we have to understand that the difference between a diesel generator and a gasoline generator has got nothing to do with the generator itself but it is the Engine driving the generator. This is absolutely crucial to understand and it will be easy to understand since we have already discussed exactly how a generator works. But just as a ‘refresher course’ let us go through it once more very quickly. Each and every type of generator works on the same principle which we remember from the previous article as the principle of Electromagnetic Induction. This basically means that in all generators there are stationary and rotatory coils called the stator containing the armature coil and the rotor which also contains coils through which direct current is passed and since the rotor rotates, this creates a rotating magnetic field which means that it creates a constantly varying magnetic flux. This changing magnetic flux is what induces an alternating current in the the stationary armature coil. Depending on the number of different poles of the rotor field coil the A.C current produced can be single-phase, 3-phase(most common having 3 different coil windings at 120 degrees separation) or polyphase current. The rotor and the rotor field coil is basically a rotating electromagnet (some small scale generators employ permanent magnets as well which are called linear alternators).
We are interested in only this rotatory motion of the rotor which is brought on by an engine connected to the rotor shaft. Although this rotatory motion can be brought about by wind turbines & other methods, we shall restrict our discussion to only Fuel driven Engines.
THE DRIVING ENGINE OF THE GENERATOR
This is the part which makes all the difference between a Gasoline driven engine and a Diesel driven engine. To understand the advantages & disadvantages of each and assessing which is better or more suited to your use will basically make the decision whether to get a gasoline or a diesel generator. It is just that simple. Before we can talk about which engine is better, we need to understand how these two types of engines work and how they use their fuel.
Both Gasoline and diesel engines are the two most commonly used internal combustion engines & even though their operations seem similar they have some interesting differences and each has advantages over the other. Both engines have the basic four-strokes intake, compression power and exhaust but there are differences between the two engines due to the different ways these two fuels burn. Gasoline readily evaporates so it gets mixed with the air efficiently & as a result, just a spark is sufficient to produce smooth combustion in a well pre-mixed gasoline engine. On the other hand diesel does not properly mix with air; however, if atomized diesel is sprayed into high-temperature air, spontaneous combustion will occur which means that in gasoline engines the fuel and air should be pre-mixed while in diesel engines mixing happens only during the combustion. This is why diesel engines use a fuel injector while gasoline engines use a spark plug. Gasoline engines are also less noisy and vibrate less compared to diesel engines because the combustion process in a pre-mixed fuel-air mixture is smooth and propagates very well but in a diesel engine the combustion could begin anywhere in the combustion chamber and it turns out to be an uncontrolled process. For this reason, to reduce the excessive vibration and noise problem, diesel engines require a more rugged structural design which make them heavier than gasoline engines. This is why gasoline engines are always preferable for lightweight applications. Since the diesel engine is compressing only the air, it can achieve a very high compression ratio without the risk of self-ignition but in a pre-mixed gasoline engine, a high compression ratio is not possible. And since higher the compression ratio the better the efficiency of the cycle(the four-stroke cycle) and this is the reason why diesel engines have better fuel economy as compared to gasoline engines.
Also, Diesel engines of the same volume can deliver a higher torque/power output than Gasoline engines.This is because Diesel has a higher energy density per unit volume than Petrol/Gasoline. Another reason behind this is the mechanics of the engines themselves.
In a diesel engine, Compression ratios are much much higher than Gasoline engines and also, since Gasoline engines use spark plugs to ignite the fuel-air mixture, the mixture burn is non-uniform. The mixture nearest the top where the spark plug is ignites first and then the burn makes its way down and out through the entire mix. However, since Diesel engines simply use compression to heat up the fuel to its flash-point(ignition temperature of a substance), the burn is completely uniform and results in driving the piston down with a lot more force than a Gasoline Engine.
In Earlier days, Diesel engines used to be much louder than Gasoline engines but nowadays, thanks to modern advances in technology, Diesel engines are almost as quiet as Gasoline ones. However, they are heavier and therefore more expensive due to the cost of material.
Diesel Engines have a very high torque but low RPM as the piston has to travel a greater distance in the combustion cylinder than in the case of gasoline engines which, while don’t put out that amount of torque have a higher RPM (piston travels a shorter distance due to the configuration of the spark-plug) & thus Gasoline engines accelerate(reach the top speed of rotation of the rotor connected to the generator) faster than Diesel ones. While this is a huge advantage in the case of automobiles, it makes no difference whatsoever in case of generators.
With diesel, you also get a lower cost of ownership. Diesel engines, and therefore diesel generators, last longer, cost less to run and take longer to depreciate in value. Diesel is also innately a lubricant which means the fuel lines, combustion cylinder interiors and other components which come in contact with the fuel will last longer and corrode/wear out lesser and more slowly than gasoline/petrol engines; perfect if the generator hasn’t been operational for a while.
However, Diesel is much less environment-friendly than gasoline as the exhaust from diesel engines are more noxious and more toxic and pollute the environment a lot more than Gasoline engines. But, on the flip-side, since lesser amounts of diesel is required to produce the same power output, over a certain period of time, the detrimental environmental effect of Diesel generators actually becomes lesser than Gasoline generators.
Next is the cost per unit volume of these two types of fuel. This is tougher to objectively say as the prices are different in each country and while in some nations, Gasoline is cheaper, in some its the other way around. Overall taking into account almost every country, the ‘world-average’ cost of Diesel is cheaper than Gasoline. This in addition to the fact that the amount of diesel required to perform the same work is lesser than Gasoline, Diesel Generators are much more cost-efficient than Gasoline ones in the long run, even though Diesel generators are more expensive than Gasoline ones.
Gasoline generators have their own advantages. You have a lot more options and models and types to choose from (since Gasoline/petrol engines have been around for a lot longer than diesel ones). Also, Nowadays, Gasoline generators are outfitted with the latest electronically controlled economy modes so as to make them more cost-efficient.
THE FINAL VERDICT
From all the above discussion and the reasoning, it is safe to say that while the competition was fierce and close, I think as a matter of personal opinion that the Diesel Generator is the winner but not by a lot. I also feel that it might vary from country to country depending on the fuel prices and also a lot depends on the usage. For industrial purposes, Diesel generators are the clear choice while for the personal home-owner, it can also come down to personal preference.
Having said all that, since the title of the article asks a question “which one to choose?”, according to the facts presented and the reasons supplied, the answer is Diesel Generators.
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