Powertrain honcho John Juriga brings us up to date
Homogeneous-Charge Compression Ignition engines have been a fascination of mine for some time, promising as they do, diesel-ish economy with gasoline-ish cost and emissions. Following a Hyundai powertrain technology briefing back in November 2013, I was pretty convinced that Hyundai’s HCCI program (which they dubbed Gasoline Direct Injection Compression Ignition, or GDCI) appeared likely to beat both the Mercedes-Benz DiesOtto concept and the GM HCCI engine to market.
Well, at this year’s Hyundai powertrain-tech shindig, I got an update from powertrain honcho John Juriga as to just whatever happened to GDCI. He explained that under compression-ignition operating conditions, the peak cylinder pressures were so great that the block and lower end (crank and bearings) needed to be strengthened to what is essentially diesel specifications, adding cost and mass. All direct-injected gas engines have some issues with particulate emissions, and these were even worse with the GDCI engine, requiring a particulate trap not unlike what Mercedes is fitting to many forthcoming S-Class engines, which eroded the hoped-for emissions aftertreatment savings. The GDCI combustion process required considerable exhaust-gas recirculation, some of which was handled by retaining said gasses in the chamber using elaborate variable valve-timing mechanisms that added cost to the top of the engine. Achieving sufficient cylinder pressures at lower engine speeds demanded fitment of a supercharger in addition to the planned turbocharger, which added still more cost (and Juriga added that electric superchargers don’t represent much of a savings relative to mechanical ones).
This litany of cost overruns left a less expensive, lower pressure direct fuel injection system as about the only remaining cost savings relative to a diesel, so the program was deemed too risky and expensive. We suspect Mercedes and GM have come to the same conclusion, as all has gone pretty quiet on the HCCI front. But all hope is not entirely lost. Being able to vary the compression ratio is a real enabler for HCCI, and indeed the Infiniti folks suggested that a second-generation of their new VC-Turbo engine might employ HCCI to clear the next round of CAFE hurdles. Keep the faith!