MOTOR Magazine

A MOTOR Magazine Newsletter
March 1, 2017

Contributed by Bob Chabot
Let’s Tech: Combustion Heats Up

Next gen combustion ignition technologies are inbound for 2018

The internal combustion engine (ICE) is something we’re very familiar with. Air, spark and fuel come together over the course of four strokes to create power and move a vehicle forward. Some may even be familiar with some of the new combustion strategies being developed. Some of them are scheduled for introduction during 2018 in 2019MY vehicles.

Mazda’s SkyActiv-G Generation 2 will introduce HCCI technology first into 2019 Mazda 3 models, and thereafter into other models. HCCI works in a similar manner to a diesel engine, using piston compression rather than a spark plug to ignite the mixture in the chamber. Here’s a brief overview of how HCCI works. (Video — Engineering Explained)

HCCI Rises Again
In a conventional ICE air, spark and fuel come together over the course of four strokes to create power and move your vehicle forward. In diesel engines, fuel is injected into the engine cylinder near the end of the compression stroke. During a phase known as ignition delay, the fuel spray atomizes into small droplets, vaporizes, and mixes with air. As the piston continues to move closer to top dead center, the mixture temperature reaches the fuel’s ignition temperature, causing ignition of some premixed quantity of fuel and air. The balance of fuel that had not participated in premixed combustion is consumed in the rate-controlled combustion phase.

But not all gasoline engines need spark plugs to ignite their fuel. There is a third type of ICE inbound — the Homogenous Charge Compression Ignition (HCCI) engine. These engines feature the same four strokes and spontaneous combustion of air and fuel, which is spread via a homogenous mixture. The two are evenly pulled into the cylinder, where the mixture is ignited by way of compression, rather than a spark, just like in a diesel engine.

This leads to lower combustion temperatures, which, in turn gives improved emissions and a more efficient engine. Think of it as the best of the gasoline and diesel worlds: HCCI can generate horsepower, gain higher fuel efficiency and produce cleaner emissions. The challenge with controlled HCCI combustion is to balance internal temperature: If it's too cold, it affects the performance of the ignition system; if it's too hot, engine knock can arise.

HCCI-based concept engines have long been under development by automakers. Examples include Mercedes’ DiesOtto, General Motors' HCCI, and Hyundai’s GDCI versions. These concepts attempted to convert gas engines to dual-mode operation using the spark plug under full load and/or idle conditions and compression ignition during steady state cruising. To date, none have made it to production series vehicles.

Interest from automakers in making HCCI a marketplace reality has been hampered by the challenge of making HCCI efficient at both low and high operating temperatures. But that hurdle has recently been overcome by companies such as Nautilus Engineering, the Ricardo Group and others, using an innovative and successful new approach — dedicated all-compression combustion ignition. This is paving the way toward controlled HCCI engines soon entering the marketplace. Mazda, for instance, announced last month it would introduce an HCCI engine in its 2019 Mazda 3 in late 2018.

A recent SAE International article reviewed Nautilus’ HCCI combustion development. It cited Nautilus CEO Matthew Riley: “Nautilus now holds patents to make controlled HCCI combustion possible for a wide range of engines. The defining feature is a piston with a top protrusion that creates the engine’s ‘primary’ combustion chamber as the piston approaches the top of the stroke. This HCCI engine will be cheaper to build than a conventional spark-ignition gasoline engine, requires no special manufacturing investment, and will return up to 30 percent improved fuel economy and near-zero NOx emissions.”

Infiniti’s VC-Turbo engine is turbocharged to increase horsepower, but can also run on the Atkinson cycle for increased efficiency. The automaker says the 2018 QX50 will equipped with the new powerplant. Here’s a brief overview of how the variable compression powerplant works. (Video — Engineering Explained)

Variable Compression Combustion Just Got Real
Infiniti’s new MR20-DDT variable compression turbocharged engine (VC-Turbo), under development for almost two decades, was first revealed at the 2016 Paris auto show, and will be available in production series vehicles by 2018. In theory, variable compression engines can alter their compression ratio. In other words, the volume of the combustion chamber when a piston is at the bottom of the stroke differs from when it reaches the top. The result is said to be an engine that can deliver the high-performance of a gasoline engine as well as the torque and fuel efficiency of a diesel.

Infiniti has turned theory into reality. Its turbocharged 2.0-liter inline-4 with direct fuel injection delivers a peak 268 horsepower and 288 pound-feet of torque — substantially better than the 208 horsepower and 258 pound-feet of torque from the automaker’s current turbocharged 2.0-liter inline-4. ““Until now, in every production engine ever built, the compression ratio has been fixed as a result of the dimensions, components and engine layout,” explained Infiniti President Roland Krueger. “The VC-Turbo engine is able to offer any compression ratio between 8:1 [typical for high performance engines] and 14:1 [used by many manufacturers for high efficiency]. The VC-Turbo engine will provide performance and efficiency comparable to, or better than, similar- or larger-sized six-cylinder gasoline powertrains.”

The engine’s compression ratio automatically adjusts to the driver’s inputs. The VC-Turbo is able to offer any compression ratio between 8:1 (typical for turbocharged engines with high boost) and 14:1 (used by manufacturers for high efficiency). Depending on the specific compression ratio, the capacity of the engine ranges from 1,997 cubic centimeters (at 8:1) to 1,970 cubic centimeters (at 14:1).

To vary compression, the engine relies on an electric motor-controlled rotating unit, called the Harmonic Drive, which leverages mechanical linkages to alter the connection between the piston and the crankshaft, so that the maximum height the piston can reach within the cylinder — and therefore the compression ratio — can be optimized. The result, Infiniti says, is an engine that delivers new benchmarks for power, efficiency, emissions, mileage and noise-vibration-harshness levels.

Koenigsegg Automotive's FreeValve engine is camless. Rather than a camshaft, it features a combustion strategy that uses actuators and software to open intake and exhaust valves. Here’s a brief overview of how the camless engine works. (Video — Engineering Explained)

Lose the Camshaft
Koenigsegg Automotive has been working on a new type of valve system for “camless” engines that completely does away with the camshaft. The Swedish supercar manufacturer conducts its engine development program through its wholly owned subsidiary, FreeValve.

“The FreeValve camless engine relies on pneumatic valve actuators to open valves, which are then closed by air pressure or springs,” shared CEO Christian Von Koenigsegg. “Each of the valves can be controlled individually, which enables infinitely variable valve lift and duration as well as easy cylinder deactivation. The pneumatic valvetrain also draws less energy than engines with conventional cams.”

CEO Christian Von Koenigsegg shared a video that describes FreeValve's approach to combustion. He noted that Chinese automaker Qoros unveiled a vehicle equipped with the FreeValve engine at the 2016 Beijing Auto Show and that once FreeValve completes refining noise levels to OEM specs, mainstream automakers will be approached. (Video — Koenigsegg Automotive)

According to Von Koenigsegg, the camless engine has already achieved reliable gains in output (up to a 30 percent increase in both horsepower and torque) and a jump in fuel economy (almost 30 percent) and a smaller, but significant, reduction in emissions as well. “Our last hurdle remaining is to reduce noise levels and integrate that into our engine. We’re very close to realizing that.”

“Overall, our goal is a camless engine that features independent control over each valve by replacing the camshaft with pneumatic actuators and software to run it,” he shared. “We also try to make sure our supercar technologies, such as engine management and combustion technologies, are capable of working just as well in normal vehicles.”

The quest for greater performance output per liter of displacement, reduced CO2 emissions, lighter vehicle weighting and other efficiencies will continue. Combustion technologies like those above have become hot properties for automakers. In addition, other more advanced technologies are being developed, such as advanced direction injection (with even more software programing) or adiabatic combustion (in which no heat is lost during combustion).

So the next time you visit a major industry event, take time to visit with companies like these that can explain the combustion changes you will soon see in your service bays. In addition, seek out trainers who can provide the associated education you'll need to service and repair these inbound technologies.

[Editor's note: Visit for the latest diagnostic and service insights.]

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