Diesel cars seem to enjoy a new wave of popularity in the USA. There are a number of reasons for that, the most important of which are the rising prices of gas. Owners of diesel cars swear that they have more fuel savings and better mileage than owners of gas-powered cars. Are there any technological reasons which make a diesel engine be more efficient over a gasoline one? Let us have a look at the diesel engine, examine how it functions, and compare it with a more conventional gasoline engine. In a gasoline engine, both the air and gasoline are sucked in and compressed with the help of moving pistons. When the spark plug fires to ignite the gasoline, the produced heat expands the air and pushes down the piston. This seemingly simple mechanism creates the power of the engine so that the car can run. However, the compression part of the gasoline engine sometimes can cause problems, as it first mixes gas with the air. Such mechanism leads to the situation when the engine only can use a limited amount of compression, because if further compression is initiated, gasoline explodes spontaneously. That knocking sound that sometimes you can hear in the engine of your car indicates spontaneous explosions of gasoline when compression rises – a bad sign showing that the engine is getting damaged. If it were possible to initiate more compression, a gasoline engine would be much more efficient and the mileage of your car would be increased. However, current gasoline technologies do not allow that. In a diesel engine, the compression problem is solved, which greatly increases the mileage and efficiency of a diesel car. Due to the facts that a diesel engine sucks in only air and does not contain spark plugs, it compresses only the air and is about twice as efficient in its compressive power as a gas engine. Diesel fuel is injected directly into the compressed air, which causes the air to heat to high temperatures and therefore to ignite the diesel fuel without any necessity for a spark. This simple change in the technological mechanism in comparison with gasoline engines allows the diesel technology to substantially, sometimes up to 50 percent, increase the efficiency of the diesel engine. There is one more big difference between these two types of engine technology – the composition of gasoline and diesel fuel. Both gasoline and diesel fuel are composed of chains of hydrogen and carbon atoms, but the chains are longer and therefore heavier in diesel fuel, which makes it weigh more than gas fuel. Due to that, if we compare the amount of hydrogen and oxygen atoms in a gallon of gasoline with the same gallon of diesel fuel, gasoline contains about 17 percent less of those atoms. Here we can come to the conclusion that a bigger number of hydrogen and oxygen atoms in diesel fuel allows it to initiate more power and makes the diesel engine more efficient than a gasoline engine. To be fair, we also have to mention some negative aspects of a diesel engine in comparison with a gasoline one. A diesel engine is bulkier and heavier because it has to deal with a great compression pressure, and, as we know, heavier engines can reduce mileage. Also, it tends to produce more soot and turns slower, which is responsible for lesser accelerating capacity of a diesel car in comparison with a gasoline car. Now, well equipped with knowledge, you only have to make a responsible driver’s choice between these two types of engines!