So you might know a bit about the combustion process, but how familiar are you with the nitty-gritty details surrounding systems of gasoline injection? We’ve come a long way from the carburetor, but even with today’s advanced methods of fuel delivery, nothing’s perfect. Let’s get into specifics of the popular Gasoline Direct Injection, or GDI design.
Playing With Fire
Combustion in a gas engine requires three elements: air, fuel, and spark. The air and fuel must be delivered in a specific ratio (and at a specific time) to the combustion chamber in order to, you guessed it, combust. There are gray areas where an engine will still run if the ratio is off, but it will either be running a fuel “rich” or “lean” mixture, causing all kinds of problems with performance, mileage and internal component wear and tear. The bottom line is, all systems of fuel injection seek to deliver this ratio as specifically and reliably as possible … but some do a better job at it than others.
Gasoline Direct Injection systems have been around since the ’50s, but GDI is considered a more modern solution owing to numerous technological improvements and wide-spread usage since then. The big difference between GDI and other types of injection is where previous systems of fuel delivery combine the fuel and air outside the combustion chamber to be brought in for combustion, GDI injects fuel directly into the combustion chamber, mixing with fresh air there for the first time. Other systems, such as Port Fuel Injection, inject fuel and air into the intake manifold, and the whole mixture is taken in through the intake valve at the right time to produce combustion. Carburetors combine fuel and air well before that and carry it through the intake valve as well.
A More Direct Approach
Injecting gas directly into the combustion chamber accomplishes a few things. Thanks to today’s very clever and responsive ECUs, fuel can be metered precisely, and high-pressure injectors allow for a spray pattern that atomizes fuel more efficiently, ultimately leading to less unburned (wasted) fuel in the chamber and more efficient combustion overall. And less wasted fuel means both better mileage and lower emissions as less unburned gasoline is leaving through the exhaust valve. This gain in mileage, performance, efficiency and environmental impact is substantial, but it does come with costs. First is the actual cost itself, components in a GDI system have to withstand high pressures and rugged conditions and as such are more expensive to produce. The other cost is potentially mechanical — the design of GDI engines lends itself to carbon buildup on the valves in the chamber and hot running conditions overall. This can result in serious damage to internal components if not addressed, and manufacturers are still searching for ways to reduce the risk. Many have found that pairing GDI with turbochargers and exhaust gas recirculation, among other technologies, helps.
All told, GDI is often simply too efficient for manufacturers to pass up. To mitigate potential problems, you should use fuel additives and intake cleaner to wash out deposits or use premium fuel to help avoid them in the first place.
Check out all the fuel and emission products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on gasoline injection, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
Photos courtesy of Blair Lampe.
Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter. In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.