Researchers in the UK have developed a new kind of engine. It could be called a hybrid, but what it combines is not two power sources but rather two mode of operation: 2-stroke and 4-stroke. The goal is to be able to significantly downsize the engine and get the fuel economy benefits of smaller displacement, but to be able to switch seamlessly to 2-stroke mode when more power is required at high loads and low speeds.
The prototype (seen above) is a modified 2.1-liter V6. After tests at the University of Brighton, it has been found to produced performances similar to a 3 to 4-liter engine, with fuel savings of 27% and emissions reduced by about the same amount.The next goal of the researchers is to incorporate the prototype engine in a vehicle.
It isn't the first time that this kind of hybrid 2/4-stroke engine design has been looked at, but in the 80s and 90s the technology simply wasn't advanced enough. "According to Ricardo, the only reason the company is able to make a viable system now is because of the software that controls the gas exchange and engine modes."
If all goes well and nothing major holds back the adoption of such a technology, it could make a big difference in the next few years. Of course, the goal is to move away from fossil fuels, but realistically, that will take a while and in the meantime a 30% improvement in efficiency would be welcome (trucks with 2-liter engines, cars with 1-liter engines). No reason why these couldn't run on cellulosic ethanol...