Diesel fuels and the future
Let's talk now about the diesel carburants. There are two main types of diesel, depending on its source:
- Petrodiesel: a hydrocarbon mixture obtained in the fractional distillation of crude oil between 250 °C and 350 °C. Diesel is generally simpler to refine than gasoline and often costs less. It contains approximately 18% more energy per unit of volume than gasoline, which along with the greater efficiency of diesel engines contributes to fuel economy (distance traveled per volume of fuel consumed). However, diesel fuel often contains higher quantities of mineral compounds and sulfur. Nowadays they are trying to reduce the amount of sulfur (ultra low sulfur petrodiesel fuel), so it will be better for the environment.
- Biodiesel: fuel made from natural, renewable sources, such as new and used vegetable oils and animal fats, (which are hydrocarbons), or even algae. Fresh soybean oil is most commonly used, although it can be made from mustard seed oil or waste vegetable oil (such as used oil from restaurant deep fryers). These hydrocarbons are filtered and mixed with an alcohol, such as methanol, and a catalyst (sodium hydroxide or potassium hydroxide), resulting in a chemical reaction whose major products are the biodiesel fuel and glycerol. It's non-flamable, non-explosive, biodegradable and non-toxic, and it's used also as an additive to petroleum diesel.
Biodiesel is one of the possible candidates to replace fossil fuels as the world's primary transport energy source, because it is a RENEWABLE fuel that can replace petrodiesel in current engines and can be transported and sold using today's infrastructure. A growing number of fuel stations are making biodiesel available to consumers, and a growing number of large transport fleets use some proportion of biodiesel in their fuel. But currently, biodiesel is more expensive to produce than petroleum diesel, which appears to be the primary factor keeping it from being in more widespread use. Besides, current worldwide production of vegetable oil and animal fat is not enough at the moment to replace liquid fossil fuel use.
The diesel equivalent to the gasoline octane rating is the cetane rating. The cetane rating number (usually 40 to 55 for medium to high speed engines) indicates how easily the fuel ignites and how fast it will burn. The rating is obtained by measuring the time lapse between fuel injection and ignition. The higher the cetane number, the easier the fuel ignites.