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The research FKFS brings to bear on its Spark Assisted Compression Ignition (SACI)  combustion process was borne from engine development work for Volkswagen's World Rallycross Championship racers. (Image: Volkswagen)

German spark-ignited compression-ignition research paralleling Mazda’s SPCCI

At SAE International’s 2018 High-Efficiency IC Engine Symposium in Detroit, the Research Institute of Automotive Engineering and Vehicle Engines Stuttgart (FKFS) revealed it is in an advanced stage of research on a gasoline-engine compression-ignition combustion system that is largely similar to Mazda’s production-ready Spark-Controlled Compression-Ignition (SpCCI) for its SkyActiv-X engine (

In a presentation at the advanced-engines conference, Andreas Kaechele said the FKFS system is dubbed Spark Assisted Compression Ignition (SACI) and the concept was borne from the nearly 90-year-old research institute’s work on high-performance engines for Volkswagen’s World Rallycross Championship (WRC) engines. The WRC engines are restricted on how much intake air is permitted, leading engine developers to examine advanced engine and combustion concepts to make the most of the available intake charge.

Kaechele said the SACI design is centered on an innovative “pre-chamber” sparkplug that ignites the fuel and propels it into the combustion chamber—amplifying the spark energy in a way that he said is crucial to controlling the auto-ignition process that creates the desired compression-ignition effect in the combustion chamber.

Mazda’s SpCCI operates under a similar concept, but uses a conventional sparkplug to initiate and more-precisely control the compression-ignition process and also to expand the compression-ignition, lean-combustion operating range.

Kaechele said test engines have operated at upwards of 7,000 rpm with a 12:1 compression ratio, 2 bar of intake pressure and a Lambda value of approximately 1.65. The engine ran on gasoline of 102 RON.

He added that test engines and simulation modeling yielded cylinder pressures up to 1.7 times those seen in the high-performance WRC engine. The testing, he said, has demonstrated new understanding of gasoline compression-ignition cylinder geometry, valve timing and fuel-injection techniques, as well as new insight into fuel’s effect on the process, saying the engine and fuel “must be accurately designed” to ensure stable SACI operation.

Kaechele did not indicate when FKFS expects to potentially commercialize the SACI system, either for production-vehicle or racing engines, but said research is ongoing.

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