Understanding Diesel Engines – Part 2

The method of combustion that is utilized by diesel engines and gas engines is one of the most significant distinctions between the two types of engines. As was said previously, combustion occurs in a diesel engine when the fuel at long last makes contact with the air that has been compressed within the cylinder. Prior to the start of the combustion process, fuel and air are mixed together in an internal combustion engine that uses gasoline. On top of that, the placement of the combustion chamber in each engine is distinct from one another. The combustion chamber of a conventional gasoline engine is located in a recess within the cylinder head (s). Combustion takes place inside the piston of a diesel engine with direct injection since the combustion chamber is located there. This combustion chamber is most frequently of the “Mexican Hat” shape, which consists of a recessed hole in the center of the piston. The term “Mexican Hat” comes from the region of Mexico where the hats were first worn. There is a protrusion in the shape of a cone located at the base of this depression. Because the fuel injector is positioned exactly above it, this protrusion is what makes it possible for the fuel to be atomized optimally and for the combustion process to be carried out perfectly. The Mexican Hat design is utilized in more than 99 percent of all diesel engines. This is owing to the fact that the core of the piston, rather than the piston crown, is subjected to the brunt of the combustion explosion. Because of this, the piston has an extremely high degree of dependability.

Injection Done Directly
Direct injection is described as an approach of fuel delivery in which the injectors of the system are made to project outward and spray fuel directly on top of the piston. There is neither a pre-chamber nor a swirl chamber, and the fuel does not have to travel through the intake manifold prior to being introduced into the cylinder. In a normal gasoline engine with several ports for fuel injection, the combustion process is more slower, more complicated, and inefficient than it is in an engine with direct injection, which makes the process much faster, simpler, and more efficient. In comparison to gasoline engines, diesels with direct injection may run at extremely low air-to-fuel ratios without negatively affecting performance. The normal air-to-fuel ratio for diesel engines is from 25:1 to 40:1, whereas the range for gasoline engines is 12:1 to 15:1. This difference might help explain why diesels have lower fuel consumption rates. A further demonstration of efficiency is provided by the fact that contemporary direct injection diesel engines inject fuel at pressures coming close to (and in some cases surpassing) 30,000 pounds per square inch (psi). This results in the most precise atomization possible, leading to a burn that is not only effective but also produces a minimal amount of waste heat.

Timing versus the Beginning of Injection
The phrase “timing” is common parlance in the world of both gasoline and diesel engines, but depending on the kind of engine you’re working with, it might refer to one of two very distinct concepts. It goes without saying that it’s essential to make a distinction between the two. Timing is the process of determining when the combustion process will begin in a gasoline engine. The timing of a diesel engine refers to the start of injection, abbreviated as SOI (when the injector begins to spray fuel into the cylinder). To reiterate, the fuel (and the injection system) is the most important component of a diesel engine. This is where it all begins and ends.

Torque. Large Amounts Of It
It is not uncommon for someone who is not familiar with diesel engines to wonder why or how diesel engines are capable of producing such incredible quantities of torque. In diesel engines, the ratio of torque to horsepower is almost never lower than 2:1, and it’s not uncommon to find ratios of 3:1 or even 4:1 in heavy-industry engine applications. The compression ratio of gasoline engines is significantly closer to being 1:1. The high amount of torque that diesel engines are capable of producing may be attributed to three primary factors: 1) the amount of boost that is provided by the turbocharger, 2) the number of strokes, and 3) the pressure inside the cylinders.

At the moment, boost pressures of 25 to 35 psi are applied to manufacturing diesel engines as soon as they leave the plant. When compared to this, a boost level of 10 psi is frequently seen as being excessive when observed in gasoline engines. Compressed intake air, also known as boost, is one of the finest things that can be used in a diesel engine since it lowers the pumping losses that occur during the intake stroke of the engine and raises the cylinder pressure that occurs during the power stroke (combustion).

In either a gasoline or diesel engine, having a crankshaft with a long “stroke” has traditionally considered advantageous for producing torque. However, why? Consider the situation as if you were using a longer wrench to loosen a bolt that was incredibly tight, as opposed to the shorter wrench that you were using before, which was unable to get the job done. If you have higher leverage, you should be able to apply more torque, right? Of course you can. Because the connecting rod of a long-stroke engine has the ability to exert greater leverage while spinning the crankshaft (when the piston is descending during the power stroke), the engine produces more torque.

During the power stroke, the sort of cylinder pressure that results in the production of torque is generated. You may have previously discovered this information for yourself. A greater amount of pressure will be generated on top of the piston if the injection event that takes place in the cylinder with an earlier start of injection (SOI) is allowed to continue for a longer period of time. When there is a bigger generation of pressure on top of the piston, there is a greater generation of torque.

Not only do high levels of boost, lengthy strokes, and extreme cylinder pressure explain why diesels are able to produce torque, but they also explain why diesel power plants are constructed with such robust components. Manufacturers use components such as deep-skirt cast-iron (and even compacted graphite iron) blocks, forged-steel crankshafts and connecting rods, and typically use cylinder heads with at least six head bolts per cylinder in order to ensure that their products are able to withstand the tremendous stresses that are placed on them. There are a lot of applications for Class 8 engines and heavy industry that favor using pistons made entirely of steel. Diesel engines are purposefully overbuilt to ensure they last a long time. After 300,000 miles of service, it is not unusual to see the factory cross-hatching still visible in the cylinders of small displacement diesels, even if the engine has been used. In addition, it is common practice for an over-the-road Class 8 engine to travel between 750,000 and 1,000,000 miles between maintenance checks.

Diesel Is Here To Stay
The combustion process, fuel injection system, and ignition system that are utilized in diesel engines are completely distinct from those that are utilized in gasoline engines. Diesel power plants have an edge over gasoline power plants in terms of fuel economy, and this advantage is one of the things that has brought diesel to the forefront of the discourse over fuel economy today. Due to the rapidly approaching CAFE standards (corporate average fuel economy standards), the buzz surrounding hybrid cars appearing to level off, and the inability of electric vehicles to provide an adequate range, more car manufacturers will turn to diesel power plants in the years to come than they ever have before. You may rest easy knowing that diesel engines are not only here to stay but also have a strong possibility of being the engine of the future. Click here to check out the best diesel fuel additives.