Honda Developing Direct-Injected Africa Twin

Direct fuel injection promises more power and lower emissions.

Africa Twin patent drawing
Patent drawings show a direct-injection fueling setup on an Africa Twin. Will we see this employed in the 2022 Africa Twin?Japanese Patent Office

We've already heard details about Honda's upcoming 2020 Africa Twin but a new patent application from the firm shows it's also developing a version of the bike with a DOHC cylinder head and direct fuel injection.

As revealed back in July, next year’s Africa Twin will become the CRF1100L with an 86cc capacity hike from 998cc to 1,084cc, upping power from 94 hp to 101 hp in the process. All 2020 versions of the bike will also get a bigger fuel tank derived from the existing Africa Twin Adventure Sports. However, Honda’s latest patent application shows a much more radical update that’s unlikely to be applied to the 2020 model but could appear at the next scheduled update in 2022.

The key changes revealed in the new patent document are a double-overhead-cam cylinder head, replacing the SOHC Unicam design used on the existing Africa Twin, and a revolutionary direct fuel injection system.

direct-injection system with dual overhead cams
This patent drawing shows the direct-injection system but also shows dual overhead cams rather than the Honda’s Unicam that is used on the Africa Twin currently.Japanese Patent Office

The direct injection (DI) is the patent application’s main thrust, and could be the solution for bike firms that are struggling to maintain the trajectory of increased power outputs in the face of increasingly tough emissions legislation. Next year, as the European Union introduces its latest Euro 5 limits, several manufacturers are taking the same route as Honda and opting to increase the capacities of their bikes. While the Africa Twin goes to nearly 1,100cc, we’ll see Triumph’s Tiger upped to approaching 900cc and there are similar rumors about KTM’s “790” twins, which are widely expected to become “890s” next year.

Why the capacity increases? Because Euro 5 rules target hydrocarbons, with a new focus on “non-methane” hydrocarbons. Those are the emissions you get when unburned fuel escapes into the exhaust, and it’s particularly hard to reduce them on high-revving, high-performance engines. That’s because high revs rely on long periods of valve overlap—when the intake valves open before the exhaust valves close—to fill the cylinders with a fresh intake charge. At lower revs, the same valve overlap gives time for unburned fuel to escape into the exhaust, causing an emissions headache.

The obvious solution—and the one favored by the likes of BMW—is variable valve timing, increasing overlap at high revs and reducing it at low engine speeds. But direct fuel injection is another way to address the issue. Instead of injecting fuel into the intake port or throttle body, direct injection means squirting it straight into the combustion chamber. It means the fuel isn’t mixed with the intake air charge until the very last moment, and injector timing becomes an additional tuning variable. So at lower engine speeds, where lots of valve overlap poses emissions problems on a conventional port-injected engine, a direct-injection system could inject the fuel a fraction of a second later so there’s no time for unburned gasoline to escape before the exhaust valves close.

It’s already a popular solution in cars; if you’ve got a C7 Corvette or a modern Camaro SS, you’re already experiencing direct gasoline injection. But on motorcycles it’s a technology that’s yet to hit the mainstream; Motus originally intended to use it on its pushrod V-4 engine, but reverted to conventional port injection before production started.

combustion chamber
Fuel is delivered directly to the combustion chamber rather than the intake ports as a measure to meet Euro 5 emission requirements.Japanese Patent Office

Direct injection isn’t a new idea, but it isn’t easy to make it work—particularly on high-speed engines. Injecting the fuel straight into the combustion chamber reduces the time available for the fuel to atomize properly and mix with the intake air charge to burn efficiently. However, the rapid adoption of the tech on modern cars mean it has come a long way since Motus tried to implement it, and provided there’s enough fuel pressure, modern injectors can achieve that elusive goal. Modern Formula 1 cars used DI to achieve somewhere in the region of 1,000 hp from their high-revving, turbocharged, 1,600cc V-6 engines, so the technology exists to make it work on similarly high-revving bikes.

Direct-injection
Direct-injection requires high pressure to deliver the fuel straight into the combustion chamber.Japanese Patent Office

Honda, as the only motorcycle firm to be making a modern F1 engine, is perfectly placed to take advantage of that knowledge. The new Africa Twin patent clearly shows that much thought has gone into getting enough fuel pressure for the DI system, with a mechanical fuel pump added on top of the cylinder head and driven from the exhaust camshaft. It works alongside the conventional electric fuel pump mounted inside the fuel tank to provide the massive pressure needed to make DI work properly.

The new DOHC cylinder head features finger followers between the camshafts and valves, in line with the latest trend in superbike engine design, reducing friction and moving valve train mass and allowing more extreme cam profiles. That’s an odd choice for an engine like the Africa Twin’s, which focuses on midrange torque rather than out-and-out power, and it could be an indication that Honda intends to use the technology featured in the new patent application on more high-performance models in the future. A future direct-injected CBR1000RR? Don’t bet against it.