Insight: Why Mazda has pursued 'dream' petrol engine technology

Homogenous charge compression ignition (HCCI) - literally squeezing the air-fuel mixture until it combusts - is standard on diesel engines but had long been impractical for petrol engines because of the different fuel characteristics. The challenge of petrol HCCI is that it works within only a limited engine rev range, which changes depending on atmospheric conditions. The ideal solution is a petrol engine that combines compression ignition with a spark ignition, enabling it to be used in a far wider range. 

A compression-ignition petrol engine is “a dream” 
for engineers, according 
to Kudo, and to achieve it Mazda extended its usual development cycle. “We used to spend two years developing each technology,” he said. “But for Skyactiv-X, we have taken five. That level of time was needed to achieve the higher target.” 

Skyactiv-X engines will enter production in 2019, twinned with Mazda’s new Skyactiv platform. Within five years of that date, Mazda will refresh its entire model range with the new engines and platform. 

Mazda has yet to set specific targets, but it is aiming for 
the new engine to combine 
the emissions and economy of a Mazda 2 with a 1.5-litre Skyactiv-D engine with the performance of an Mazda MX-5 with a 2.0-litre Skyactiv-G petrol unit. 

Although Mazda is continuing to pursue combustion engine advances, it isn’t shying away from electric. It will introduce a mild hybrid and a battery EV in 2019 - and, by 2035, every Mazda sold
 will have some element of electrification. Progress in that area will be aided by a recent technical tie-up with Toyota. 

Again, there is a difference: Mazda’s focus is on ‘well-to-wheel’ emissions, which accounts for how the energy that goes into a vehicle is created. In that context, an EV is only clean if the energy powering it comes from a clean source. 

“We’re not denying electrification,” said Fujiwara. “By making CO2 savings on the combustion engine, we can reduce the burden on
 the hybrid.” The exact level
 of electrification in Mazda’s line-up will vary from country to country, taking into account power sources and legislation. 

A petrol engine with reduced emissions and improved economy can require a smaller electric hybrid unit, removing some of the packaging challenges of the system. 

Kudo said: “If the required motor and battery is small, we can provide customers with
 a small, cheap and compact hybrid system with very good fuel consumption.”