Diesel Engines: Fueling Your Knowledge

One of the best inventions created would have to be an engine. Look at the contributions this machine made to the world and how it pushed us forward as a society. Since its conception, the engine has come a long way. Powering our different modes of transportation, such as planes, boats, cars , bikes and trains. Even though they all have a similar concept, they all work differently, especially in the type of fuel they use. But today let’s talk about one type of engine, using a specific type of fuel. A combustion engine that uses diesel fuel. Diesel engines are great for many reasons, but also come with its drawbacks, let’s get into how they work.

What you will learn:

How diesel engines work :

What is a diesel engine?

A diesel engine is a type of combustion engine that uses diesel fuel to be powered. There are two types of combustion engines. One of which is a gas engine which ignites compressed air and gas with a spark plug to perform the power stroke. These combustion engines have what we call a four stroke cycle. This cycle produces mechanical power. The power stroke is the third stroke that’s a part of the four stroke cycle. This power stroke is the main thing that puts the second type of engine, the diesel engine in its own category. It’s about how diesel engines work when it comes to the power stroke.

The first stroke of the piston moves down simultaneously, sucking air into the cylinder’s combustion chamber through the intake valve, which opens when the 1st stroke occurs. The second stroke of the piston moves upward, via the crankshaft and compresses that air to a very high degree. This reaction makes the air very hot. The higher the piston goes, the hotter the air. The piston moves all the way to the top, which is called “Top Dead Center”. Now the air is at an optimal temperature of heat. Hot enough for the beginning of the third stroke. Just before the piston’s position on the second stroke reaches the top, diesel fuel is then injected into the cylinder from the top. The fuel mixes into the hot air and then an explosion takes place, pushing the piston downward for the third stroke.

This third stroke is called the power stroke or “Bang” from the “S.S.B.B”. After reaching the bottom, “Bottom Dead Center” the pistons move back upward for the forth stroke via the crankshaft. The forth stroke pushes the exhaust from the explosion out of the cylinder’s combustion chamber, through the exhaust valve which opens as the forth stroke occurs. The first and third strokes are what differentiates gas from diesel engines. The first stroke in a gas engine sucking in air, is mixed with fuel. Whereas, in a diesel engine it’s just air. The third stroke/powerstroke in a gas engine, uses a spark from a spark plug to ignite the fuel and air mixture for the explosion. Whereas, in a diesel engine the air is compressed further and then ignited with the introduction of diesel fuel, when the air is hot enough for the explosion.

Is a diesel engine better than gas?

There are a couple areas where diesel engines outperforms gas engines. Areas like fuel economy and Utility. Diesel engines experience more compression pressures because of its compression based system. Therefore diesel engines have to be built with stronger beefier engine internals. Stronger beefier engine components means that it weighs more, therefore it cant rev as high as a gas engine. This may seem like a disadvantage at first glance however, this makes diesel engines last longer than gas engines, while still revving the engine less. This brings us to another point, where diesel engines don’t need to rev as high because it makes all of its power early on in the rev range.

Diesel engines have more torque than gas engines because of its compression based ignition system. Diesel engines naturally produce more torque, making it ideal for hauling towing applications like pickups and trucks. Diesel fuel also has more energy than gas, making it also more fuel efficient than gas engines. Gas has 15% less energy in it for the same volume of diesel fuel. The combination of the compression based ignition system and diesel fuel, makes the diesel engined vehicles outperform gas engine vehicles in the area of efficiency. Diesel engines can go as much as 20-35% more distance on an equivalent gallon of fuel. The compression based system in a diesel engine, compresses the air fuel mixture more than a gas engine would.

This process gets more energy out of the same amount of air, making it more efficient in this aspect. As a result, diesel engines use less fuel than a gas engine. Although Diesel engines have these benefits, it may not be enough to outway the potential harm or disadvantages. One disadvantage is price. Diesel engines are more complex, making them more expensive in the used and new vehicle market than gas engine vehicles. The infamous dieselgate scandal, played its own role in changing related laws and taxation.

That made it tough for a good resale value of diesel powered vehicles in markets across the world. Also to add, the emissions equipment in diesel cars are quite expensive to replace, especially if the vehicle is used. These disadvantages contribute to a lot in the decision making when looking for a diesel vehicle, potentially outweighing the benefits. In order for diesel vehicles to make more sense over a gas engine, your situation would have to call for you driving a lot. You have to cover more miles in order to feel the benefits of fuel efficiency over the gas engine. Otherwise, you’re better off getting a gas powered vehicle.

Do diesel cars accelerate faster?

A car’s acceleration from a stand still, has a lot to do with how much torque it has. A good combination for a fast accelerating car off the line, is if the car is relatively light and also has high amounts of torque. Diesel engines produce more torque naturally over gas engines. This is so, because diesel engines use a compression system for engine combustion in which it compresses air to an optimal amount of heat for combustion. That being said Diesel engines use slightly more air for compressing. It does this by an engine design that allows the pistons to travel slightly further up and down relative to its width.

This engine design produces more torque early on in the rev range. This makes the perfect conditions for faster accelerating, especially from a stand still. However, because of this engine design, diesel engines weigh more. The added weight on the engine, prevents it from revving as high as a gas engine would. Gas engines revving higher allows for more horsepower, which is great over a longer distance for speed. Simply put, the diesel engine would be quicker off the line but the gas engine would catch up over a distance.

Types of diesel engines :

Three main diesel engines?

The three main types of diesel engines are classified by size such as small, medium and large. These engines are the same as gas engines but put into a size category. For instance you have engines such as a 4 cylinder, V6, V8, V12’s etc. Four cylinders and V6’s are considered small, whereas V8’s and V12’s are considered medium sized. Large engines are the ones that power ships and trains

Diesel engine problems :

Why are diesel engines not used ?

There are a few factors that dictate whether a product is widely used or not. One of which is price. Because of the complex nature of diesel engines and extra pressure the engine internal components experience from the combustion ignition system, diesel engines cost more to produce. The diesel engines need heavier and beefier parts, which are more materials. This drives the cost up for manufacturers and customers. Manufacturers make less money to sell and customers pay more to buy.

Another area where price affects diesel engines is in the resale value. Especially after the dieselgate scandal, related laws and taxation changed, making resale values weak for diesels on the used market. It is also expensive to maintain a used diesel car, because of complex emissions equipment. The health harming pollutants diesel engines produce require complex emissions equipment to control this. The price to replace this can oftentimes be 15% to 30% of a used car value.

Three disadvantages of diesel engines?

Although diesel engines have a lot of benefits, the disadvantages outway the benefits in certain scenarios. Most of the disadvantages of diesel engines have to do with cost. Three main disadvantages of diesel engines are :

• Engine complexity 

Diesel engines are more complex and use more materials to make. This drives the cost up for consumers of diesel engines, while also producing less profit for manufacturers. 

• Pollution

Although gas engines produce more CO2, diesel engines produce more health harming pollutants like soot particles and Nitrogen Oxide. Because of these pollutants, diesel engines require complex emissions equipment, which are quite expensive especially when the car is used. Owners may try to get around this issue cheaply, which may result in more pollution on used diesel engines, because of not so easy access to proper emission controls. Another point is that diesel engine manufacturers produce more pollutants, because of the complex nature of the engine’s design.

• Resale Value

Diesel engines have weak resale value on the used car market, due to an increase in awareness of related pollution for this engine type. Especially after the dieselgate scandal, this changed certain markets that used to have a strong resale value for diesel engines. That scenario, coupled with diesel engines costing more to purchase when new, isn’t quite good.

Why is diesel unpopular in the US ?

Diesel fuel is more expensive than gas, even more than premium fuel at times. This can definitely change the attitude towards diesel engines in the US, making it unpopular. The supply and demand also drives the price up for diesel engines as well. Another reason is certain laws and taxes related to environmental restrictions, put diesel fuel prices at another disadvantage.

Biggest drawbacks of a diesel engine?

The biggest drawbacks of diesel engines have to do with engine complexity. This leads to a whole host of other issues, which turn into disadvantages for the diesel engine. The diesel engine complexity leads to higher costs to manufacture the engine, which simultaneously causes more pollution because of more materials being used. This means diesel engines cost more for the consumer while the manufacturer profits less. Diesel engines also require complex emissions equipment to control pollutants. This equipment can be very expensive, especially if you have a used diesel powered vehicle. This expensive emissions equipment can lead to corners being cut to save money, which inturn makes it worse for the environment if propper pollution controls aren’t in place.

Conclusion

Diesel engines have become a part of the conversation of combustion engines whether you like it or not. Although it’s exceptional when it comes to fuel economy, it also raises concerns for environmental reasons. Most applications for diesel engines are used for heavy duty applications, where you can really squeeze the benefit of fuel economy out of it. Our buses, trains, ships , farm equipment, construction equipment, mostly things that are constantly on the move, covering large amounts of miles, get the benefit from diesel engines. Otherwise for smaller applications like commuter cars, it will mostly make financial sense to go with a gas powered vehicle, as opposed to a diesel engine.