This upstream location provides ample time for full vaporization to occur. One downside is that fuel droplets sometimes are deposited on the intake port walls, upsetting the intended fuel-air ratio.
With DI, the chance of detonation—premature ignition of the fuel and air mixture—is diminished because the phase-change cooling effect takes place during the compression stroke just before ignition. Ford raised peak torque by 30 lb-ft in its new 3. There are downsides to DI. A DI system is more expensive because the pressure required to squirt fuel into the combustion chamber is 50 to times higher than with PI, and the higher-pressure pump imposes parasitic losses.
Direct injectors tend to be noisy. Carbon deposits—both on the backsides of the intake valves and on tailpipes—are service issues for some DI users. These carbon particles are similar to but smaller in size than those spit out by diesel engines. Toyota, for example, fires both injectors during low to medium load and rpm conditions—in other words, during normal driving. This raises the density of the incoming charge without boosting and flushes carbon deposits off the intake valves.
During high load and rpm circumstances, when maximum combustion chamber cooling is needed because detonation is more likely, DI handles all the fuel delivery. Ford uses PI alone at idle and at low rpm for smooth, quiet, and efficient engine operation. As rpm and load increase, fuel delivery becomes a programmed blend of PI and DI. Somewhere along the line, the intake charge is mixed with fuel before the spark plug makes it all go boom inside the combustion chamber.
This is all ICE for most of you, I'm sure. Back in the ancient days of engine technology, the carburetors and single-point fuel injection systems did their relatively imprecise air and fuel mixing in or even before the intake manifold, adding about the right amount of fuel for entire bank of cylinders. For the most part, each combustion chamber got the what it needed. However, depending on the design of the intake manifold, this approximation could result in the cylinders closest to the carb or fuel injector getting a bit too much fuel running rich while the cylinders farthest away got a bit too little running lean.
A skilled carburetor tuner or smart engine computer could keep things from getting out of control, but even the best tune was limited by the design of the intake manifold. The vast majority of modern cars use a multi-point fuel injection MPFI setup also known as port injection. Here's how it works: rather than using one injector that sprays about the right amount of fuel, each of the individual intake runners has its own injector or injectors that adds a squirt of aerosolized fuel to the intake air from a pressurized injector.
The air and fuel mixture is drawn into the open port and into the combustion chamber by the retreating piston. The intake valve then slams shut, and the explosive combustion happens in the now sealed cylinder. For the most part, MPFI is just fine and dandy. It's certainly much more efficient than the older carburated and SPFI systems thanks to its capability to adjust the amount of fuel added to the intake for each individual cylinder, equalizing the formerly lean and rich cylinders at the extreme ends of the manifold, improving power generation, and reducing wasted fuel.
So, why fix what's effectively not broken? How does direct injection improve performance? You may have noticed that during the jumps from carburetion to SPFI to MPFI, the point at which fuel is added to the intake charge has moved from before the throttle to the intake manifold and onward to the individual intake runners -- closer and closer to the combustion chamber.
Direct injection takes this evolution to the next level by placing the injector inside the combustion chamber. By moving the injector into the combustion chamber, gasoline direct injection GDI gains a few advantages over the previously discussed systems. A GDI system also has more flexibility regarding when in the combustion cycle the fuel is added.
MPFI systems can only add fuel during the intake stroke of the piston, when the intake valve is open. GDI can add fuel whenever it needs to. Magazine Current Issue Past Issues. Connect with us. Advertise Subscribe Contact Us. By Brendan Baker. Direct-injected engines also are afflicted by a condition called low-speed pre-ignition LSPI. The injectors usually are located in the runners of the intake manifold. Click to comment.
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