Good things happen when you let engineers go play in the sandbox. Everything from intermittent wipers to bed-extending tailgates are the result of a good idea appropriately implemented, and Mitsubishi wants to be the next to add a little pioneering mechanical know-how to a common problem. This time, the automaker is tackling incomplete fuel combustion in direct-injected engines like the one in the 2026 Outlander, which leads to increased emissions.
The challenge, then, is to improve combustion, allowing the engine to make more power with less fuel while also cutting down on soot. Best of all, Mitsu’s recently patented idea seems pretty simple, comprising a new design for the piston crown and little else.
Direct Injection Poses Some Problems
Direct injection system animation of injector spraying fuel at idle.Direct injection system animation of injector spraying fuel. (Source: MotoLogic)
In a direct-injected internal combustion engine, the fuel injector is located in the combustion chamber, near the intake valve and spark plug. Unlike a port-injected or throttle-body-injected engine, where the fuel and air mix together before entering the cylinder, a direct-injected mill requires the gasoline to intermingle with the fresh air coming in through the intake valve a mere instant before compression and combustion happen.
That part of the process is called tumble flow, and it’s very much like it sounds; air tumbles into the cylinders via the intake valve, and a specialized piston design causes it to swirl around and mix with the fine mist of gasoline from the direct fuel injector. The issue that Mitsubishi identified, however, is that some of the fuel gets pushed away from the ignition source (the spark plug,) such that when it fires, some fuel doesn’t get consumed. The result is worse fuel economy and increased emissions from the unburned fuel turning into fine particulates – i.e. soot.
In its patent, Mitsubishi has a relatively simple solution: a new piston crown with an inclined surface angled toward the fuel injector, positioning the gasoline droplets closer to the spark plug at the time of combustion. It sounds a little complicated, so let us try to break it down.
How Does The New Piston Crown Work?
Mitsubishi piston crown patent for direct-injected enginesMitsubishi / United States Patent and Trademark Office
Looking at the cylinder from directly above, we can place the intake valve on the “northwest” corner and the exhaust valve positioned “northeast.” The fuel injector sits at due west, and the spark plug hangs out above it all in the dead center of the combustion chamber. The piston fills almost all the circumference of the cylinder, and it has depressions on the northwest and northeast sides to accommodate valve movement.
A conventional direct-injected piston features a trough cut into the crown, which sort of captures and concentrates the fuel spray. Mitsubishi’s patented design, however, ditches the lake and replaces it with a sledding hill. An inclined surface runs down the piston crown from west to east, its slope matching the angle of the fuel injector’s installation, with two raised edges perpendicular to the slope in order to effectively guide the fuel down the incline.
Mitsubishi piston crown patent for direct-injected enginesMitsubishi / United States Patent and Trademark Office
Mitsubishi says this design is better at stabilizing the tumble flow effect, leading to more complete combustion of the fuel when the spark plug fires. As an added bonus, the company also incorporates a small, perforated covering for the spark plug, with a pre-ignitor that sends a compressed flame front through the perforations and into the cylinder. We’ve seen pre-chamber ignition used before on Maserati’s Nettuno V6 engine and on the facelifted 2026 Jeep Grand Cherokee’s new turbocharged 2.0-liter engine.
Base Trim Engine
1.5L I4 Hybrid
Base Trim Transmission
2-speed CVT
Base Trim Drivetrain
Front-Wheel Drive
Base Trim Horsepower
177 HP @6000 RPM
Base Trim Torque
207 lb.-ft. @ 3600 RPM
Infotainment & Features
9 /10
CarBuzz Insight – Why This Matters:
The net result of the design is improved emissions and fuel economy, as well as more power – in theory, at least. Mitsubishi hasn’t announced if its fancy new piston crown will ever see the light of day, but we think it’d make good sense on whatever vehicle will follow the 15-year-old Outlander Sport compact SUV.
Whether or not that’ll happen remains in question, however.
Source: United States Patent and Trademark Office
