Is variable compression ratio engine now in use?

Yes, variable compression ratio (VCR) engines are currently in use, though they are not yet widespread. Manufacturers like Nissan and Infiniti have introduced models featuring this technology, which allows the engine to adjust its compression ratio for optimal efficiency and performance. The technology aims to enhance fuel economy and reduce emissions while maintaining power output. However, VCR engines are still in the early stages of adoption in the automotive market.