Chinese manufacturer BYD has launched a high-efficiency version of the 1.5-liter Xiaoyun engine, dedicated for use with PHEVs.
The new engine is specifically built to accommodate the company’s DM-i hybrid technology, with a brake thermal efficiency (BTE) of 43%; its makers claim this makes it the world’s most thermally efficient gasoline engine in production.
Eric Li, deputy general manager of BYD Auto Sales, commented, “BYD has always insisted on self-reliance to build its core technology. With our advantages in new energy technologies, we have achieved major breakthroughs in several key areas. The DM-i hybrid will rigorously accelerate the replacement of traditional fuel cars with new energy vehicles.”
In order to achieve such an impressive level of thermal efficiency, BYD says it has used a compression ratio (CR) of 15.5, an increased B/S (Bore to Stroke) ratio, an Atkinson cycle for improved combustion efficiency, an exhaust gas recirculation (EGR) system, and a series of friction-reducing measures.
In addition, the Xiaoyun engine takes full advantage of the electrification of plug-in hybrid models, electrifying accessories and removing the traditional front-engine accessory drive system, further improving efficiency.
The company states it has also implemented a split cooling system for the first time. Through on-demand cylinder head and cylinder block temperature measurements, the cooling provision can be actively managed to ensure optimal running temperatures. BYD notes that mitigating heating losses shortens the warmup cycle after a cold start by 15-20%, reducing fuel consumption and carbon emissions during the process.