Some interesting tidbits about Mazda's new Skyactiv-D technology. They're planning on replacing the current 2.2L with this new 2.2L which sports a 20% increase in fuel economy (they say it'll give 43 mpg on the hwy, no mention of what vehicle thats in). It has 14:1 compression ratio, the lowest of any passenger car diesel engine. It says that the lower compression ratio allows for better air/fuel mixing and optimized combustion timing. The article also explains how a higher compression ratio is needed for cold starts, but Mazda got around it by using variable lift on the exhaust valves. It keeps them open during cold starting to increase cylinder temps and thus the cold start ability. The lower compression ratio also lead to lighter weight components taking 6.6 lbs off the internal's weight. It also has an aluminum block which saves another 50 lbs over the previous engine.
Mazda ‘Reinvents’ Diesel With New Skyactiv-D