Determine the specific weight of diesel

What you need:

• Spring balance
• Graduated cylinder
• wire

Basic information about diesel

• Before starting to determine a specific weight of the substance, first something basic about diesel and why it is important to know this value.
• The fuel known as diesel is a mixture of various hydrocarbons that is suitable for being burned in diesel engines. The name of the fuel is reminiscent of Rudolf Diesel, who invented these engines.
• Biodiesel is esterified rapeseed or soybean oil. This substance is also suitable for the operation of the engines, but from a chemical point of view it is a different substance.
• In order to know the usefulness of the fuel, the calorific value is important, because this indicates which can be used energy is in the substance.
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• Diesel has a calorific value of 42.5 MJ / kg and biodiesel one of 37.2 MJ / kg. Since you don't buy fuel based on weight, but rather on volume, this information is of little use to you. You are interested in the amount of energy that can be used per liter.


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• A specific weight indicates how much weight there is per unit volume. If you know this size, you can calculate what weight a liter of diesel has and what mass. Since the substances are mixtures, there are also fluctuations in weight.

Determine the specific weight of the substances

1. Use wire to attach a bracket to a measuring cylinder so that you can hang it on a spring balance.
2. Measure the weight in N of the empty vessel by hanging it on the scales. Make a note of the value.
3. Now fill exactly 100 ml of diesel into the container. Make a note of this weight.
4. Subtract the two values ​​to find the weight of the diesel.
5. The specific gravity is the quotient of the weight by the volume. Assume that the diesel oil has a weight of 0.81 N and a volume of 100 cm³, then the specific weight of diesel is 0.0081 N / cm³. Taking into account the location factor, you arrive at a density of 0.82 g / cm³ = 0.82 kg / l.
6. Do the same for biodiesel. You get a density of 0.88 kg / l.
7. Now you can compare which substance has a higher calorific value per liter. 42.5 MJ / kg * 0.82 kg / l = 34.85 MJ / l (diesel), 37.2 MJ / kg * 0.88 kg / l = 32.74 MJ / l.

In practice, the density of diesel varies from 0.82 to 0.84 g / cm³ and that of biodiesel from 0.87 to 0.88 g / cm³.