The gasoline internal combustion engine has been in service for well over a century at this point. After all that time, you would think we would have perfected it by now. It’s as simple as suck-squeeze-bang-blow, right? But recently we’ve seen a number of new technological advances that each offer significant gains to efficiency—probably a good thing considering how long it is going to take to move to an all-electric light vehicle fleet.
The latest one I’m enthusiastic about was cooked up by Delphi and Tula. Called Dynamic Skip Fire, the new tech should work with most any gasoline engine, boosting fuel efficiency by up to 15 percent.
There’s life in the ICE
Back in 2016, we discovered that Mahle had managed to perfect an idea called Turbulent Jet Ignition, which has pushed the thermal efficiency of current Formula 1 engines up to an unheard of 47 percent. Until then, the Toyota Prius engine was considered top dog with a thermal efficiency of ~40 percent.
From there, a pair of breakthroughs soon came from Japan. Infiniti figured out how to alter the compression ratio of a cylinder on the fly in its new VC-Turbo engine. As a result, the new QX50 uses a 2.0L inline-four instead of a 3.7L (naturally aspirated) V6, but it generates more torque and gets 27mpg instead of just 20mpg.
And rival Mazda managed to perfect compression ignition, an idea that plenty of other OEMs had spent fortunes on before abandoning as unworkable. Mazda’s Skyactiv-X Spark Controlled Compression Ignition engines aren’t quite production ready, but they’re coming. Along with boosting engine efficiency, they ought to benefit drivability, too.
Skip to the beat
Dynamic Skip Fire isn’t quite as magic a bullet for improving fuel efficiency—Delphi says it should improve things by between 7 and 15 percent. But it could be incorporated into the design of any modern engine pretty easily for only about $350 per engine.
It’s a cylinder deactivation method, but one that’s a lot more advanced than the version you might have encountered in recent vehicles from General Motors, Alfa Romeo, Aston Martin, Audi, or even Ferrari. Let’s take GM’s LT1 as an example. When it’s in the right mode and the engine load is light, the valve lifters on half its eight cylinders are deactivated, temporarily turning the engine into a V4. But it’s always the same cylinders that get shut off, which has led some to worry about differential wear rates of engine components. On top of that, some engines can create unpleasant vibrations across certain rev-ranges during cylinder deactivation.
By contrast, Dynamic Skip Fire is, well, dynamic. Every cylinder in the engine can be deactivated via a mechanism that prevents the cam from actuating that cylinder’s valves. A coprocessor runs alongside the engine’s electronic brain, deciding whether to deactivate any given cylinder. This could be every 90 degrees of crankshaft rotation in a V8 or every 180-degrees for an I4. In addition to engine load, the processor also takes into account the NVH (noise, vibration, harshness) characteristics of the engine when deciding to deactivate a particular cylinder.
Because any cylinder in the engine can be cut, the system is able to ensure that temperatures remain constant across the engine, and premature wear on some cylinders compared to others shouldn’t be a problem. Delphi says that Dynamic Skip Fire can boost fuel efficiency by around seven percent when used with an I4 engine and 15 percent with a V8.
It works so well I couldn’t tell it was running
A few weeks ago I got to experience the system at work, installed in one of Delphi’s test mules—in this case a four-cylinder Volkswagen Passat. As with the best technology demos, it was remarkably unremarkable. As we drove around a mix of roads near the US Capital—including a brief run on I-395 as well as 25mph city streets—a display showed that the system was working, cutting all four cylinders at times as we decelerated to a stop. Coupled as it was to one of Delphi’s 48v mild hybrid systems, it felt like any other Passat. It wasn’t slow, and it didn’t vibrate or sound weird—it just worked.
Now, this isn’t the sort of system you or I could buy on the aftermarket and fit to our own cars, but it is the sort of thing that an OEM could add to an existing engine range without much difficulty. It doesn’t cost much, either—Delphi reckons it would add around $350 to an engine. GM had previously invested in Tula, and it’s the first OEM to adopt this tech, calling it Dynamic Fuel Management. It will debut in MY2019 Chevrolet and GMC trucks with either 5.3L or 6.2L V8 engines.
Listing image by John F. Martin for Delphi