Much of what you hear from Pike Research is focused on alternatives to the gasoline-fueled internal combustion engine (ICE). Yet, as we often point out, gas-fueled ICE vehicles will remain the dominant vehicle through this decade and likely well into the next. With hybrids and turbochargers, the efficiency of ICE vehicles will increase significantly. However, the basic design of four-stroke engines with pistons pushing on a camshaft and valves for exhaust and air has remained relatively unchanged for decades. I’m not saying this to shortchange the engineering work that has gone into improving these engines – that has been substantial – but the basic architecture is the same.
Now, a couple of start-up companies are looking to change the design of motors in interesting ways. Scuderi Group has designed what they call a split cycle engine. In this design, the compression stroke and the power stroke are separated. Once these strokes are separated, the compression cylinder can be reduced in size which improves compression efficiency. The air crossover tube provides air to the power cylinder. The power cylinder sees greatly reduced temperatures post combustion which reduces nitrogen oxide (NOx) emissions in comparison to typical four-stroke engines. The result is a four cylinder engine with two power cylinders and two smaller compression cylinders.
To improve efficiency, the Scuderi engine can still take advantage of a turbocharger. But Scuderi claims that to truly improve efficiency, they can add a high pressure air tank between the compression and power cylinders (something they refer to as an “air hybrid”). This air tank permits the engine to shut off the compression cylinders and use air from the tank to provide air to the combustion chamber. It also allows the engine to shut off the fuel supply during idling or braking and use compressed air from the tank for the power stroke. This turbocharged, air hybrid Scuderi engine has been tested to produce 65 mpg with 85g/km of CO2 emissions in a European high economy class vehicle, a 25% improvement in comparison to the average of 52 mpg and 104g/km of CO2 in this class.
Another design from EcoMotors transforms the engine to have two opposing cylinders with opposing pistons. So, the pistons are essentially pushing against each other during compression. The engine is still a four-stroke engine, but thanks to the moving pistons on each side of the cylinder, valves are no longer necessary, simplifying design of the engine. EcoMotors claims up to 50% increase in fuel efficiency with their motors, with 50% fewer parts. They have partnered with a Chinese firm, Zhongding Holding (Group) Company, Ltd., to manufacture and commercialize the engine.
When will we see these technologies in passenger cars on American roads? With the high fuel economy rules coming, I would not bet against some special applications of these technologies. However, car companies spend hundreds of millions of dollars to develop and test new engines over many years. Even if one signed up today, I wouldn’t expect to see it in a vehicle prior to 2017 model year. And other designs are competing for the R&D dollars in automotive firms, including rotary and turbine engines.
In my conversation with Sal Scuderi, he pointed out that of the 170 million engines sold per year, only 60 million of these are used in automotive applications. The rest are power generation or other stationary applications. Both Scuderi Group and EcoMotors are targeting this stationary market. I believe this is logical first step since the safety and durability issues are more easily controlled in stationary applications. New engine designs are more likely to be accepted in these markets. But if the new designs prove as reliable, efficient, and cost effective as claimed in stationary applications (or in emerging automotive markets like China or smaller vehicles like scooters), expect to see movement towards non-typical designs in the automotive market, as well.