The oil has the particular characteristic that when it is extracted in its pure state it has a lot of organic compounds intermingled. This is logical if we think that the most accepted theories about the origin of oil speak of the decomposition of living beings over a large number of years. In petroleum, we can find all kinds of "aliphatic" hydrocarbons, which are those that are composed only of hydrogen and carbon, the two primordial components of the microorganisms and plants that probably originated them.
The properties of the different components of an oil change with their composition, thus, methane (natural gas), propane and butane are gases that we use for heating, while the heavier cyclohexane or benzene are liquid. In order to separate the different components in the oil refineries, they heat them, in this way those simpler molecules will evaporate in the first place, to then evaporate the most complex and heavy ones.
The first fraction that evaporates is known as naphthas and is composed of molecules that have five, six, and seven carbons, used as solvents. Then the molecules that have between seven and eleven carbons are separated, which are the ones used to obtain the gasoline, all here at a lower temperature than the boiling point of the water.
Then the components of kerosene and diesel, which have between twelve and fifteen carbons are separated. Then we can find lubricating oils, with a boiling point much higher. For example, the engine oil may be operating all day at 120 ° C without evaporating the least. And to finish the process, the bitumen and the tar used for the asphalting of roads are extracted.
Difference between Diesel and Gasoline
Thus, as it corresponds to its greater number of carbons, diesel is heavier than gasoline and evaporates much more slowly, but has much more calorific power. Thus, a gallon of diesel (3.8 liters) has 155x106 Joules of energy, while the same amount of gasoline has 132x106 Joules of energy.
Due to this greater power and a better combustion process, diesel is 30% more efficient than the same amount of gasoline. Although we must also take into account that it is necessary 25% more oil to make diesel, so if we look at the efficiency of a fuel based on the "oil equivalents" a diesel engine would allow us to do 20% more mileage that one gasoline
The differences between both types of fuel do not end here, we must also take into account also the environmental consequences of each of them. Gasoline produces a greater amount of carbon dioxide (CO2), since you have to burn more to get the same result as diesel, which contributes more to the greenhouse effect, while diesel fuel produces more oxides of nitrogen and soot, which on the other hand can cause acid rain and smog, or photochemical haze, which can be seen in the vicinity of large urban centers.
Gasoline engine
When we speak of a gasoline engine (also called an explosion engine), we are faced with a type of internal combustion that obtains mechanical energy directly from the chemical energy of a fuel. The explosion of the fuel by means of a spark produces the expansion of the gas, which finally causes the movement of the piston.
There are two and four times and the thermodynamic cycle used is known as Otto Cycle. This cycle is applied in internal combustion engines by means of the electric spark mentioned. An invention of the German engineer Nicolaus Otto in 1876. As we said a little above, there are two-stroke engines (1 turn of the crankshaft) and four-stroke engines (2 crankshaft turns). In the first case, also called cycle engine, the gas change is directed by the piston, not as in the 4-stroke that is by valves. In the second case, with the four-stroke engine, four strokes of the piston are required (intake, compression, combustion or explosion and exhaust) to complete the combustion cycle.
Diesel engine
The diesel engine was invented in 1893 by the German engineer Rudolf Diesel. In this case, we are facing a thermal engine, that is, transforming heat into mechanical work through the temperature gradient between a heat source (hot focus) and a heat sink (cold focus). Diesel engines have internal combustion, a type of machine that obtains mechanical energy directly from the chemical energy of a fuel that burns inside the combustion chamber. Possibly we are facing the key that most differentiates both concepts: the combustion process. While in petrol engines the process arises from a spark inside the cylinder (and by means of the spark plug), in diesel engines the combustion process arises from the high temperature that reaches the air in the phase of compression (so high that it is sufficient to ignite the fuel when it comes into contact with the hot air).
Therefore, the compression ratio is very different in both engines, since diesel need compressed air to reach a higher temperature in order to ignite the fuel. In addition, the fuel supply system works at much higher pressures compared to gasoline engines.
Difference between gasoline and diesel
- The types of gasoline are defined by the octane this is no more than the measure that anti-knock gasoline has. Detonations and ensure maximum energy release in internal combustion engines.
- Diesel oil, on the other hand, differs according to its quality, type A is of higher quality, while the type that is of the lowest quality
- Diesel fuel releases up to 10% more energy than gasoline. The diesel fuel consists of paraffin while the gasoline is composed of a mixture of various hydrocarbons