A test engine which is based on this idea is similar in some ways to a highly efficient diesel engine, but runs on petrol. The company has tested the technology in a single-piston test engine under various operating conditions. They have started testing the technology on a multi-cylinder engine which is close to a production engine.
Its fuel economy estimates shows that engines based on this technology could be far more efficient than even diesel engines. These estimates are based on simulations of how a medium sized vehicle would perform with a multi-cylinder version of the new engine.
The Delphi technology is the latest attempt by researchers to combine the best qualities of diesel and petrol engines. Diesel engines are 40 to 45 percent efficient in using the energy in fuel to propel a vehicle, compared to roughly 30 percent efficiency for petrol engines. But diesel engines are generally dirty and require expensive exhaust-treatment technology to meet emissions regulations.
For decades, researchers have attempted to run diesel-like engines on petrol to achieve high efficiency with low emissions. Such engines might be cheaper than hybrid ones since they don't require a large battery and electric motor.
In conventional petrol powered engines, a spark ignites a mixture of fuel and air. Diesel engines don't use a spark. Instead, they compress air until it's so hot that fuel injected into the combustion chamber soon ignites. Several researchers have attempted to use compression ignition with petrol, but it's proved challenging to control such engines, especially under the wide range of loads put on them as the car idles, accelerates, and cruises at various speeds.
Delphi's approach, which is called petrol-direct-injection compression ignition, aims to overcome the problem by combining a collection of engine-operating strategies that make use of advanced fuel injection and air intake and exhaust controls, many of which are available on advanced engines today.
For example, the researchers found that if they injected the petrol in three precisely timed bursts, they could avoid the rapid combustion that's made some previous experimental engines too noisy. At the same time, they could burn the fuel faster than in conventional petrol engines, which is necessary for getting the most out of the fuel.
They used other strategies to help the engine perform well at extreme loads. For example, when the engine has just been started or is running at very low speeds, the temperatures in the combustion chamber can be too low to achieve combustion ignition. Under these conditions, the researchers directed exhaust gases into the combustion chamber to warm it up and facilitate combustion.
The engineering manager of advanced powertrain technology at Delphi Powertrain suggests that the engine could be paired with a battery pack and electric motor, as in hybrid cars, to improve efficiency still more, although he also mentioned that it's not clear whether doing that would be worth the added cost.
Photo credit: delphi.com