Introduction to the Types of Diesel Truck Engines
Mar 16th 2022
The world runs on diesel. Diesel engines power all kinds of large industrial vehicles, including buses, ships, trains, and trucks. They are the preferred choice when it comes to towing, hauling, and lifting. But not all diesel truck engines are created equal. Some drivers and towers swear by certain types of diesel engines, while others shop around for the best deal. But each type of engine comes with its own pros and cons. Learn about the different types of diesel truck engines and how they’re used in various industries today.
What Is a Diesel Engine?
Let’s start by defining a diesel engine. Diesel engines use compressed air and fuel to start the internal combustion process. The fuel ignites when it interacts with a high-temperature highly compressed gas mixture containing oxygen. This is what’s known as the diesel cycle, which is named after Rudolf Diesel, who invented the first diesel engine in 1892. The process converts chemical energy into mechanical energy, which then powers the vehicle.
Traditional gas-powered vehicles also use internal combustion, but instead of compressing the air and fuel, they use spark plugs to ignite the fuel, which powers the engine. Instead of a spark, a diesel engine uses glow plugs to heat the incoming air and fuel before it enters the combustion chamber. This helps the engine burn the air-fuel mixture at the proper temperature.
Diesel engines are more powerful than gas-powered engines to help you haul heavy loads even at low speeds. That’s why these vehicles tend to be used as work trucks. They tend to be common in the construction, mining, and agricultural industries.
A diesel engine produces more energy with the same amount of fuel because the heat stays in one place. Diesel fuel also contains more energy per molecule than gasoline fuel, which explains the added cost at the pump.
Diesel vehicles are required to comply with strict emissions standards. Most engines use some type of exhaust after-treatment method to reduce harmful emissions that contribute to pollution and climate change. These systems rid the exhaust gas of toxic pollutants before releasing the exhaust into the atmosphere. Many diesel engines use Cummins exhaust gas recirculation (EGR) coolers to reduce the temperature of the exhaust as it gets recycled through the engine. They also use selective catalytic reduction (SCR) to convert NOx into gases that occur naturally in the atmosphere. These parts require additional maintenance, but they ultimately help the engine last longer than a traditional gas-powered engine.
Diesel engines are sold as part of commercial and passenger vehicles. They are made by Powerstroke, Duramax, and Cummins. Powerstroke creates engines for Ford trucks, including the Super Duty line. Duramax engines are found in Chevy Silverado 2500 and 3500, and Cummins engines are used in the Dodge RAM 2500, 3500, 4500, and 5500. Each type of engine offers unique benefits, but auto manufacturers continue to compete with one another, so these engines tend to be on par with one another.
How Does a Diesel Engine Work?
All diesel engines consist of at least one piston and one cylinder. They operate using a two-stroke or four-stroke cycle. The main difference between gas-powered and diesel engines is that diesel engines induce the compressed air during the intake stroke. The energy is created when the burning fuel is injected or sprayed into the hot, compressed air in the cylinder. The air must be hot enough to ignite the fuel or the combustion process won’t work. Air temperatures usually reach 526°C (979°F) or higher. The cylinder can produce additional heat as well.
The entire diesel cycle consists of four steps:
During induction, the piston sucks air in as it moves down the bore and opens the inlet valve. Air pressure should be between 1.7 and 2.4 megapascals when it gets inducted into each of the cylinders.
Once the inlet valve closes at the bottom of the stroke, the piston will rise and compress the air inside. The air doesn’t mix with the fuel until it reaches the cylinder. Compressing the air helps prevent pre-ignition problems that are mostly found in high-compression spark-ignition engines.
Diesel engines use fuel-injection systems that produce injection pressures between seven and 70 megapascals (1,000 to 10,000 pounds per square inch). Fuel gets inserted into the cylinder at the top of the stroke, which then forces the piston down, allowing for ignition. The fuel then mixes with the hot, compressed air, where it ignites upon impact. The fuel injection process must be precise. Injection must begin when the piston is near top dead center. The fuel is burned in a nearly constant-volume process while the piston is open. As the piston moves away from this position, fuel injection continues as the injectors supply near-constant pressure.
There are different kinds of fuel injection systems. Direct injection is the most common. This means the fuel gets injected directly into the combustion chamber directly above the piston.
During combustion, the piston will move upward, so the exhaust valve can open, which lets the burned gas flow out of the cylinder. Many diesel engines use an after-cooling system known as exhaust gas recirculation (EGR). The exhaust gas gets recirculated instead of leaving through the exhaust. The EGR system then pumps coolant near the gas to transfer excess heat to the radiator where it gets burned off naturally. EGR reduces the amount of NOx emissions that reduce air quality and increase pollution.
The EGR is about more than just reducing harmful environmental toxins. It will also help you prevent excess wear and tear. Too much heat can damage your engine. The EGR cooler lowers the temperature of the exhaust fuel to keep the fuel from damaging internal parts and components.
Shop for Replacement EGR Coolers Online
Diesel engines operate with either two-stroke or four-stroke cycles. Diesel engines usually come with compression ratios between 14:1 to 22:1. Both two-stroke and four-stroke engine designs can have bores (cylinder diameters) less than 600 mm (24 inches). Engines with bores of greater than 600 mm are almost exclusively two-stroke cycle systems.
Many diesel engines are also turbocharged, which provides additional power and improves fuel efficiency. The air compressor or blower increases the amount of compressed air in the cycle, which lets the engine burn more fuel per cycle for an extra jolt of power on the road.
Different Types of Diesel Truck Engines
There are several ways to categorize diesel engines. They are usually listed as small, medium, or large based on power output.
- Small Diesel Engines
Most diesel engines are small, which means they have power-output values of less than 188 kilowatts, or 252 horsepower. They are commonly found in trucks, automobiles, agricultural equipment, and some generators. They are typically direct-injection, in-line, and have four- or six-cylinders. Many are also turbocharged and come with exhaust aftercoolers.
- Medium Diesel Engines
Medium-sized engines have power-output values of 188 to 750 kilowatts, or 252 to 1,006 horsepower. They are most often found in heavy-duty industrial trucks. They are usually direct-injection, in-line, and have six cylinders. They are also turbocharged and aftercooled. Some V-8 and V-12 engines also belong to this size group.
- Large Diesel Engines
Large engines come with power-output values of more than 750 kilowatts. They are often found in large industrial vehicles, including locomotives and marine vehicles, as well as large-scale generators. They also tend to be direct injection, turbocharged, and have aftercooled systems.
You can also list diesel engines based on whether they have a two-stroke or four-stroke cycle.
- Two-Stoke Diesel Engines
Two-stroke engines have a simpler design than four-stroke engines. They often eliminate the need for one or two valves. Intake air and the exhaust can pass through ports in the cylinder liner, which reduces the need for more valves. Two-stroke engines weigh less than four-stroke engines. They also tend to be cheaper and easier to maintain with fewer diesel parts.
These engines are also more energy efficient. They produce power once for every rotation instead of once every two rotations, which is the case for four-stroke engines. However, that can also put more wear and tear on the cylinders, which usually requires more aftercooling and lubrication. You will need to replace your diesel parts more often than you would if you were using a four-stroke.
You won’t find many two-stroke engines on the road. They tend to be found in large industrial vehicles, like locomotives and marine vessels. Two-stroke engines also tend to be noisier than four-stroke engines and may generate more smoke.
- Four-StrokeDiesel Engines
With four-stroke engines, the intake and exhaust valves and the fuel-injection nozzle are located in the cylinder head. These often use dual valve arrangements, including two intake valves and two exhaust valves. They tend to be heavier and more costly to maintain than two-stroke engines.
Most diesel engines are four-stroke, including the ones you find in most automobiles.
Replace Your Diesel Particulate Filter to Keep Your Diesel Engine Running Strong
What Is the Best Diesel Truck Engine?
Now that you know a thing or two about diesel engines, let’s look at some of the leading makes and models on the market today and what makes them so popular.
Cummins has been making reliable diesel engines for the Dodge RAM line of trucks for years. In 2008, the company released the 6.7L Cummins to replace the 24-valve 5.9L Cummins to comply with the country’s latest emission standards. It was rereleased in 2013 with SCR (Selective Catalyst Reduction), an advanced form of aftercooling that reduces the amount of harmful toxins in the air. SCR injects a special liquid reductant, usually Diesel Exhaust Fluid (DEF), into the exhaust stream, which sets off a chemical reaction that converts nitrogen oxides into nitrogen, water, and tiny amounts of carbon dioxide (CO2), natural components of the air we breathe, which is then expelled through the vehicle tailpipe.
Today, the 6.7L Cummins is considered the best diesel engine for towing. It produces peak torque of 1,075 lb./ft.
6.7L Cummins Specs:
- Max. Horsepower: 420 hp @ 2,800 rpm
- Max. Torque: 1,075 lb-ft @ 1,800 rpm
- Bore x Stroke: 4.21 x 4.88 inches
- Valvetrain: OHV with 2 valves per cylinder
- Engine Weight: 1,060 lbs (dry)
- Aspiration: Turbocharged and Charge Air Cooled
You will still need to replace your EGR cooling system after a while, especially if you are doing some heavy towing. If you are still using the 5.9L Cummins, find a new EGR Cummins cooler online to reduce the amount of NOx emissions coming out of your tailpipe. The 5.9L was known for having a defective cooler, which is why the company decided to upgrade it in the first place.
The EGR cooler on the 6.7L Cummins is much more reliable than the one on the 5.9L, but you may still run into issues from time to time. Find a replacement Cummins 6.7L EGR cooler to resolve the issue.
If you’re driving a Ford truck, you can’t go wrong with the 6.7L Powerstroke. Ford used to partner with International Navistar when developing its engines, but the 6.7L is the first design the company made all by itself. The new version resolves many of the problems that were found in the 6.0L and 6.4L Powerstroke engines. It can produce up to 475 HP, and 1,050 lb./ft. of torque. It’s considered the best engine for Ford trucks.
6.7L Powerstroke Specs:
- Max. Horsepower: 475 hp @ 2,800 rpm
- Max. Torque: 1,050 lb-ft @ 1,800 rpm
- Bore x Stroke: 3.89 x 4.25 inches
- Valvetrain: Conventional pushrod OHV with 4 valves per cylinder
- Engine Weight: 990 lbs (dry)
- Aspiration: Single VGT turbocharger
If you are still using the 6.0L Powerstroke, your EGR cooler will likely fall apart over time. The seals could leak coolant into the exhaust as blue smoke comes out of your exhaust. The excess heat will only damage your engine over time. Find a replacement 6.0L EGR cooler online to keep your exhaust the right temperature.
If you are looking for the most reliable diesel engine on the market today, you will want the 7.3L Powerstroke engine. Ford once again partnered with International Navistar to create a signature line of diesel engines for heavy-duty trucks. This engine uses Hydraulic Electric Unit Injection (HEUI), which eliminated the need for a dedicated injection pump. It uses high pressure engine oil to create hydraulic pressure within each injector.
7.3L Powerstroke Specs:
- Max. Horsepower: 275 hp @ 2,800 rpm
- Max. Torque: 525 lb-ft @ 1,600 rpm
- Bore x Stroke: 4.11 × 4.18 inches
- Valvetrain: OHV (overhead valve) with 2 valves per cylinder
- Engine dry weight: 920 lbs (dry)
- Aspiration: Single turbocharger, Garrett GTP38 (wastegated)
6.6L Duramax L5P
If you’re driving a Chevrolet or GMC truck, you will need to go with the 6.6L Duramax. It was introduced in 2017 as a way of helping the company stay relevant in the diesel market. It comes with revised cylinder heads, an updated camshaft, and a new variable-vane turbocharger for better fuel efficiency on the road. It gets a total of 445 horsepower and 910 lb./ft. of torque.
6.6L Duramax L5P Specs:
- Max. Horsepower: 445 hp @ 2,800 rpm
- Max. Torque: 910 lb-ft @ 1,600 rpm
- Bore x Stroke: 4.05 x 3.89 inches
- Valvetrain: OHV with 4 valves per cylinder
- Engine Weight: 835 lbs (dry)
- Aspiration: Electronically controlled and actuated variable geometry turbocharger
Consider what type of engine is under the hood when buying a diesel truck. This will tell you a lot about the vehicle and its limitations. Take these specs with a grain of salt, considering horsepower, torque, fuel economy, and towing capacity are largely determined by the make and model. The two-wheel drive model will always be lighter and more fuel efficient than the four-wheel drive model. The larger your diesel truck, the more it will tow, but you will lose fuel efficiency as a result. Consider which qualities are most important to you when finding the right engine.
The diesel engine has come a long way since it was first invented over 100 years ago. Keep these diesel engines in mind when looking for the best truck money can buy.
Virrage Images / shutterstock.com
Li Van Goh / shutterstock.com
VFXartist / shutterstock.com
Bubbers BB / shutterstock.com
Redcollegiya / shutterstock.com