Mazda Sees 'Super-lean-burn' Engine in 2019 (1)

2017/09/15 14:17
Naoshige Shimizu, Nikkei Automotive
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Mazda's new engine

Mazda Motor Corp will commercialize a next-generation gasoline engine that combusts fuel by "compression ignition (CI)" instead of "spark ignition (SI)" in 2019.

Mazda made this announcement Aug 8, 2017. It plans to drastically improve thermal efficiency by realizing "super lean burn" with an air-fuel ratio of about 30 or higher (excess air ratio: 2 or higher). Mazda President Masamichi Kogai defines the next-generation engine as the "second round of the engine revolution," planning to use it as a base technology for "reducing CO2 emissions to the utmost limit."

Mazda calls the next-generation engine "Skyactiv-X." Compared with the existing gasoline engine using the "Skyactiv-G" first-generation technology, the Skyactiv-X is expected to improve the fuel efficiency of an engine by up to 20-30%. And the torque is expected to be improved by 10% on average for the entire range and by up to 30%.

Mazda plans to realize the super lean burn by expanding the validity range of HCCI (homogeneous-charge compression ignition) combustion, which compresses air-fuel mixture for multi-point ignition. The HCCI is a dream technology that many engineers and researchers have tried to realize but have not commercialized yet due to its narrow operation range.

In the low-load range, the cylinder temperature does not increase much, making it impossible to ignite fuel. On the other hand, in the high-load range, fuel burns too violently. In the high-rotation range, ignition cannot catch up with the fast piston movements.

Mazda developed a technology called "SPCCI (spark-controlled compression ignition)" to expand the operation range of the super lean burn (compression ignition) to include the entire practical range. Though the company has not yet disclosed the details of the technology, it seemingly aims at increasing compression ratio to increase temperature and pressure in cylinders and realizing a new kind of combustion that performs compression ignition at multiple points while using ignition plugs.

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