Why do some diesel engines run on diesel fuel and others on fuel oil?

Question

Trucks and smaller vehicles with diesel engines run on diesel fuel which looks more or less like kerosene - less flammable than gasoline, low viscosity liquid. However larger diesel engines like this 120 thousand horsepower marine engine have more or less the same design but use fuel oil which looks very different from diesel fuel - much higher viscosity and I'd guess igniting fuel oil at room temperature is a challenge.

How does it happen that engines of the same design use two different fuels? If one of them is superior to the other then why won't they all stick to that superior fuel?

Answer 1

Have you looked at the size of one of those maritime diesel engines? They are larger than your car and need to deliver a lot of power to move and power the ship. That takes a lot of fuel so it's cheaper to burn more cheaper fuel even if it is of inferior quality. The bigger size also lets it use wider fuel lines so the viscosity is less of an issue. You also need to heat fuel oil to be able to pump it around.

Cars use diesel because emission regulations and fuel economy. The narrow regulations of diesel fuel lets the manufacturers design the engine to burn just that fuel as efficiently and as cleanly as possible. There is also a size constraint on car engines. So more viscous fuel would be an issue and take up precious space for wider fuel channels and heating elements to keep the oil liquid.

Cost per ton per mile just works out better to use diesel for trucks and cars while fuel oil works out better for the large ships.

Answer 2

A diesel engine for a car needs a fuel which is liquid even in winter. This fuel should contain a very small amount of sulfur to limit air pollution.

The marine bunker oil is not liquid at room temperature, it has to be heated to about 50 °C before pumping out of the tank and to about 130 to 140 °C before injecting it into the cylinders. It contains a lot of sulfur, a lot of harbours do not allow it to be used inside the harbour because of the air pollution. The ship needs an extra fuel tank with diesel oil for the harbour and for the cold start of the engine. The bunker oil has to be pre heated after a cold start before it could be used.

Answer 3

Simple economics. Marine engines consume enormous amounts of fuel, so in order to reduce operating costs, they use the cheapest, least desirable sludge that the oil refineries can produce.

Answer 4

Diesel engines can run on a wide variety of fuels, as long as the fuel provides some lubrication.

https://en.wikipedia.org/wiki/Fuel_oil#Uses

Residual fuel oil is less useful because it is so viscous that it has to be heated with a special heating system before use and it may contain relatively high amounts of pollutants, particularly sulfur, which forms sulfur dioxide upon combustion. However, its undesirable properties make it very cheap. In fact, it is the cheapest liquid fuel available. Since it requires heating before use, residual fuel oil cannot be used in road vehicles, boats or small ships, as the heating equipment takes up valuable space and makes the vehicle heavier. Heating the oil is also a delicate procedure, which is impractical on small, fast moving vehicles. However, power plants and large ships are able to use residual fuel oil.

Answer 5

Diesel and heater oil are the same thing , the tiny difference is the additive package ( a fraction of 1 % of the total). Diesel may have a better additive to prevent wax from crystallizing and plugging lines in cold weather , for example. From time to time in various locations there may be different limits on sulfur ; depending on the refinery this may or may not result in different S levels in the products. Heavy marine fuel is a different from diesel because marine engines have heaters to reduce the viscosity of heavy oils like "bunker C".