Understanding Your Diesel Engine

These days, the performance gap between diesel and gasoline-powered engines has begun to narrow due to a number of advancements. These developments include different types of fuelling strategies, air charging technology, self-cleaning mechanisms, and emission-reduction measures.

So, whether you plan to purchase your first diesel vehicle, or you’re already the proud owner of one, you’ll probably want to know: how exactly they work, what their unique advantages are, and how to keep your diesel engine in pristine condition.

First off, let’s cover the basics of diesel engine technology.

How diesel engines work

Both gasoline and diesel engines are Internal Combustion Engines (ICEs). The term internal refers to the inside of the engine, while combustion refers to the chemical reaction that occurs between substances in the combustion chamber.

An internal combustion engine is a heat engine. It is a system that converts heat to mechanical energy, which is then used to do mechanical work. In an ICE, the combustion of fuel occurs with an oxidizer (usually air) in the combustion chamber. As a result, the expansion of the high-temperature and high-pressure gases produced by the combustion applies direct force to the piston.

This is different to how External Combustion Engines (ECEs) work. An ECE burns fuel outside of the engine to heat water and produce steam. The pressure of the steam moves a piston back and forth inside a cylinder. The kinetic energy of the moving piston is used to turn the vehicle’s wheels, the turbine, and other mechanical devices.¹

Figure 1 http://saerulmajapahit.blogspot.com/p/kurikulum-pendidikan-seorang-mekanik-ok.html.

What’s the difference between gasoline and diesel engines?

In a gasoline engine, air enters the cylinder via the intake port and inlet valve. Alternatively, air can be pushed under pressure by a turbo or supercharger, and the fuel added to the air charges the cylinder. In recent times, fuel can be directly injected into the cylinder with GDI (Gasoline Direct Injection) technology, which allows for more precise fuel control and delivery.

From there, the piston compresses the air from atmospheric pressure to a much higher pressure. Then, the mixed air and fuel inside the cylinder is charged to a higher temperature. Upon ignition the heat is suddenly released. As a result of the oxidization, the rapid heat release expands the combined mixture, pushing the piston down.

Diesel engines are a bit different. First, air enters the cylinder. Then fuel is introduced at the right time to ignite and release through the hot compressed air. The average compression ratio of a diesel engine is between 14:1 and 25:1, while the average compression ratio of a gasoline engine is between 8:1 and 12:1.

Next, fuel droplets are sprayed into the combustion chamber via a fuel injector. Here, the air gets so hot, oxidation takes place immediately – without need for a spark plug – and the resulting expansion pushes the piston down.

Benefits of diesel engines

Figure 2 Khalili, N.R., P.A. Scheff, and T.M. Holsen, PAH source fingerprints for coke ovens, diesel and, gasoline engines, highway tunnels, and wood combustion emissions. Atmospheric environment, 1995. 29(4): p. 533-542.

✔ Greater fuel efficiency – Research shows that diesel fuel has 10 to 15 percent more energy density than gasoline, which produces more mileage per gallon (3.7 litres) in the same conditions. Diesel engines also have greater thermal and volumetric efficiency, as well as lower pumping losses as they operate in wide open throttle condition VS gasoline engines.

✔ Longer lifespan – Diesel engines are more durable than gasoline engines, because they can withstand higher compression ratios and they operate in lower engine revolution. They also do not have spark ignition components, such as sparkplugs and ignition coils, which need replacing.

✔ Better performance – When in the same condition as a gasoline engine, a diesel engine generally produces more torque. The result is not only less fuel consumption – with a partial or full load in comparison to a gasoline engine – but also higher torque, which achieves a lower engine revolution. This translates into a sudden power gain even in low engine speeds.

✔ Clean and reliable – More diesel engines are starting to include self-cleaning Diesel Particulate Filters (DPFs). On longer drives, when the engine is hot enough, the DPF will automatically remove harmful exhaust-produced particles, as well as the production of incomplete combustion (known as soot). When the DPF is regularly maintained, this greatly helps in the reduction of Exhaust Particulate Matter (EPM).²

Regularly maintain your diesel vehicle

Just like a gasoline vehicle, regular maintenance of your diesel vehicle – at the recommended manufacturer service intervals – is vital to a consistently safe, smooth, and reliable drive. It will also help improve the lifespan of your pride and joy.

You should also be sure to use only the highest quality diesel-specific oils, filters, and coolants. Or let your trustworthy and reliable mechanic take care of this essential task for you, saving precious time and worry.

At Car Servicing & You we give you honest, reliable advice about what your car needs, and what it doesn’t. We have locations in Carnegie, Ormond and Keilor Park for your convenience. Book online today and we’ll take care of the rest.

¹ Merker, G.P., Reciprocating Engines, in Combustion Engines Development. 2012, Springer. p. 9-37.

² Van Setten, B.A., M. Makkee, and J.A. Moulijn, Science and technology of catalytic diesel particulate filters. Catalysis reviews, 2001. 43(4): p. 489-564.