How fuel injection brought fuel delivery out of the 1800s
07 May 2020
In the 150-year history of the modern automobile, there has been a multitude of fuel delivery variations from the evaporative canister of the 1886 Benz Patent Motorwagen to the highly-computerized fuel injection of current production cars. The new technology allows for more efficiency and power than ever before, but do the manufactures have it all figured out perfectly? Not quite, as explained by Jason Fenske of Engineering Explained.
In order to best understand the progression of fuel injection, it is best to start with how a basic carburetor works. The key is the venturi effect, where a slight restriction in the airflow increases air velocity and drops air pressure. Fenske’s whiteboard drawing is a great illustration of the basic system, which can get complicated awfully quickly in practice. The air velocity increase and pressure drop pull fuel from the float bowl through a metered orifice (commonly called a jet) and mixes the fuel with air before it enters the intake manifold and then the combustion chamber where its burned.
It is a relatively long path for the fuel droplets to be suspended in the moving air, and even distribution has always been difficult on multi-cylinder engines. So the natural progression is to transition to fuel injection with multiple injectors, one per intake port, that are closer to the intake valve. This allows more precise metering of fuel on a cylinder-by-cylinder basis, which is better for emissions and power. So if closer to the combustion chamber is good, better has to be in the combustion chamber, right?
Sort of. Direct injection, as it is called, is yet another leap in efficiency and power potential, but as soon as production cars starting racking up street miles a drawback was found. Gasoline is a solvent, and removing it from the airstream in the intake manifold allowed a significant buildup of grime on the back of the intake valves. The easiest solution was actually a small step backward, combining port injection with direct injection. Tune the system extremely carefully and you have a fuel-sipping engine that also remains clean.
The main takeaway is that on a functional level the classic carburetor is fine. I like to think of it as a carpenter’s hammer. You can decide to have only a carpenter’s hammer in your toolbox and complete plenty of projects just fine. If you add a body hammer to the tool chest though, certain tasks will be completed better and more efficiently. That body hammer requires a different skill to operate, but once mastered it can be leveraged to do great things. The car world has given us lots of tools to choose from and each has their place in helping us create engaging and efficient cars.
Courtesy of Hagerty