The humble car engine operates through a thermodynamic principle called the Otto cycle. Named after German engineer Nicolaus Otto, the process involves compressing fuel to turn it into gas that produces force to turn a mechanism. Otto’s work had been critical in building the first cars in the late 19th century—and is still essential now.
Over the years, the automotive industry has come up with various layouts to optimize fuel use and performance. Some arrange the pistons in different configurations, while others add more pistons to increase power. Knowing the type of engine a particular car model uses determines the kind of repair and maintenance necessary.
Fuel Type (Gasoline, Diesel, and Hybrid)
The first step in any repair or maintenance work involves knowing the kind of fuel the engine runs on. Until the late 1990s, vehicles had either a gasoline or diesel engine under the hood. They might look the same outside, but they’re distinct in the way they operate.
One of these distinctions is thermal efficiency, which determines how much heat gets put to work. Although gasoline and diesel come from the same crude oil, the latter is denser and contains 15% more energy. Such density translates to more power when combusted, around 40% more efficient in converting fuel to mechanical energy. Diesel engines usually don’t need spark plugs for ignition, relying on compression instead (though they accept glow plugs for operating in cold conditions).
However, diesel doesn’t burn as clean as gasoline due to the latter’s high volatility point and low flashpoint. Gasoline engines burn almost every batch of fuel every cycle, which reduces the burden on the catalytic converter. As a result of this clean burn, gasoline engines enjoy the benefit of low-cost operation and ease of repair and maintenance.
Hybrid engines grant two sources of propulsion: a gasoline or diesel engine and an electric motor. The engine still assumes the role of driving the car for long journeys, but the electric motor supplies energy for specific tasks like starting the car. Because hybrid engines are a relatively new technology, the industry’s still figuring out the most efficient way to fix and maintain them.
The average car owner or buyer wouldn’t be able to tell the difference which car runs which. That’s why they ask for help from experts when they browse vehicles or bring their cars to a repair shop.
Cylinder Layout (Inline, V-Type, and Boxer)
Next is the cylinder layout. This can influence specific features like the vehicle’s weight, the type of cranks, firing sequence, and engine block design.
The most widespread is the inline or straight configuration, found in standard cars, compacts, and hatchbacks. The cylinders are perpendicular to the vehicle, positioned side by side. To balance out the forces generated by combustion, the cylinders fire in pairs, starting with the inner two cylinders. With a higher center of gravity, inline engines provide stability when driving.
The V-type layout features cylinders arranged in two opposite banks, set at an angle between 60o (V6 and V8) and 90o (V8). This arrangement cancels the up-and-down motion of each piston, which gives it stability. The additional cylinders provide more performance, but the compartment has to be spacious enough to accommodate them. V-type engines are more common in performance cars and large diesel vehicles like SUVs and trucks.
The boxer or flat configuration is the least prevalent of the three, only built by select manufacturers. The cylinder layout is at a full 180o, balancing the forces as its low center of gravity distributes its weight evenly. Their rarity in the industry owes to its intricate design; not all spare parts work well with this configuration, making repair or maintenance work a pain.
Number of Cylinders
Did you know that the Guinness World Record for the most number of cylinders in a street-legal vehicle is 48? Of course, this vehicle borders on impracticality, being so large that it needs a different engine to start it.
Before the era of turbochargers and fuel injection systems, the number of cylinders determined the engine’s overall output. They still do today, though not as much, because even a turbo-four engine can power a pickup truck. Instead, this aspect of engine design determines engine efficiency, fuel economy, and ease of maintenance and repair.
Without turbo, the four-cylinder setup offers a balance of fuel efficiency and performance. When configured inline, these cylinders won’t generate as much noise as other engines, making them the prime choice for an average family car. Because inline-fours are a dime a dozen, maintaining and repairing them is a breeze.
Six and eight-cylinder setups require the V-type configuration (although several manufacturers are known to have built inline ones). As mentioned earlier, arranging the cylinders at the optimal angle gives the engine stability. Even engines with over eight cylinders, such as V12 and V16, are still configured this way.
Some compact car models only carry two or three cylinders under the hood, owing to their small size. Turbochargers and fuel injection allow their engines to provide almost the same performance as inline-fours but using less fuel. The three-cylinder setup, however, suffers from rattling because of torque imbalance. As such, manufacturers often build engines with an even number of cylinders.
Engine Orientation (Front, Mid, Rear)
Mass production vehicles have their engines out front for several good reasons, the most important being that they’re front-wheel-drive (FWD) vehicles. The engine’s weight provides stability when accelerating. However, FWD systems make the car prone to understeer, losing traction when the weight shifts to the rear wheels.
Mid and rear engines are more common in performance vehicles and supercars, as they have rear-wheel-drive (RWD) systems. RWD vehicles are incredible race cars because the traction originates from the rear axle, resulting in higher acceleration. But just as FWD cars are prone to understeer, RWD ones are prone to oversteer.
It’s fascinating to see how far the engine has developed, now coming in a variety of builds. It shows that carmakers continue to improve their craft, finding ways to make the most out of every drop of fuel consumed. Given the industry’s technology roadmap, it won’t come as a surprise if future engines will feature an inline-eight or V24.