Automakers Show Interest in an Unusual Engine Design
The Scuderi engine could substantially improve fuel consumption by storing compressed air.
An engine development company called the Scuderi Group recently announced progress in its effort to build an engine that can reduce fuel consumption by 25 to 36 percent compared to a conventional design. Such an improvement would be roughly equal to a 50 percent increase in fuel economy.
Sal Scuderi, president of the Scuderi Group, which has raised $65 million since it was founded in 2002, says that nine major automotive companies have signed nondisclosure agreements that allow them access to detailed data about the engine. Scuderi says he is hopeful that at least one of the automakers will sign a licensing deal before the year is over. Historically, major automakers have been reluctant to license engine technology because they prefer to develop the engines themselves as the core technology of their products. But as pressure mounts to meet new fuel-economy regulations, automakers have become more interested in looking at outside technology.
Although Scuderi has built a prototype engine to demonstrate the basic design, the fuel savings figures are based not on the performance of the prototype but on computer simulations that compare the Scuderi engine to the conventional engine in a 2004 Chevrolet Cavalier, a vehicle for which extensive simulation data is publicly available, Scuderi says. Since 2004, automakers have introduced significant improvements to engines, but these generally improve fuel economy in the range of something like 20 percent, compared to the approximately 50 percent improvement the Scuderi simulations show.
There’s a big difference, however, between simulation results and data from engines in actual vehicles, says Larry Rinek, a senior consultant with Frost and Sullivan, an analyst firm. “So far things are looking encouraging—but will they really meet the lofty claims?” he says. Automakers should wait to see data from an actual engine installed in a vehicle before they license the technology, he says.
A conventional engine uses a four stroke cycle: air is pulled into the chamber, the air is compressed, fuel is added and a spark ignites the mixture, and finally the combustion gases are forced out of the cylinder. In the Scuderi engine, known as a split-cycle engine, these functions are divided between two adjacent cylinders. One cylinder draws in air and compresses it. The compressed air moves through a tube into a second cylinder, where fuel is added and combustion occurs.
Splitting these functions gives engineers flexibility in how they design and control the engine. In the case of the Scuderi engine, there are two main changes from what happens in a conventional internal-combustion engine. The first is a change to when combustion occurs as the piston moves up and down in the cylinder. The second is the addition of a compressed-air storage tank.
In most gasoline engines, combustion occurs as the piston approaches the top of the cylinder. In the Scuderi engine, it occurs after the piston starts moving down again. The advantage is that the position of the piston gives it better leverage on the crankshaft, which allows the car to accelerate more efficiently at low engine speeds, saving fuel. The challenge is that, as the piston moves down, the volume inside the combustion chamber rapidly increases and the pressure drops, making it difficult to build up enough pressure from combustion to drive the piston and move the car.
The split-cycle design, however, allows for extremely fast combustion—three to four times faster than in conventional engines, Scuderi says—which increases pressure far faster than the volume expansion decreases it. He says that fast combustion is enabled by creating very high pressure air in the compression cylinder, and then releasing it into the combustion chamber at high velocities.
Having a separate air-compression cylinder makes it easy to divert compressed air into a storage tank, which can have a number of advantages. For one thing, it’s a way to address one problem with gasoline engines: they’re particularly inefficient at low loads, such as when a car is cruising at moderate speeds along a level road. Under such conditions, the air intake in a conventional engine is partly closed to limit the amount of air that comes into the engine—“it’s like sucking air in through a straw,” Scuderi says, which makes the engine work harder.
In the new engine design, rather than shutting down air flow, the air intake is kept wide open, “taking big gulps of air,” he says. The air that’s not needed for combustion is stored in the air tank. Once the tank is full, the compression piston stops compressing air. It’s allowed to move up and down freely, without any significant load being put on the engine, which saves fuel. The air tank then feeds compressed air into the combustion chamber.
The air tank also provides a way to capture some of the energy from slowing down the car. As the car slows, the wheels drive the compression cylinder, filling up the air tank. The compressed air is then used for combustion as needed.
It is still far from clear whether the design can be a commercial success. Even if the simulation results translate into actual engine performance in a car, the engine may not prove to be easy and affordable to manufacture, Rinek says, especially with equipment in existing factories. The design will also have to compete with many other up-and-coming engine designs. Scuderi says the first application of the engine might not be in cars, but instead as a power generator, especially in applications where having compressed air on hand can be useful. For example, construction sites can require electricity for power saws and compressed air for nail guns.