Compression test

The spark ignition engine is constantly evolving, but could a move to gasoline direct-injection compression-ignition technology help reduce carbon, NOx and particulate emissions and increase fuel efficiency?

Powertrain engineers are continually seekingways to improve the combustion engine, driven by the demand for better efficiency and performance. This has brought us to where we now stand with a market dominated by downsized, turbocharged gasoline engines.

But as regulations tighten, especially in terms of NOx and particulate emissions, and pressure increases to reduce the amount of CO2 emitted from vehicle tailpipes, not to mention a push for greater fuel efficiency, new approaches will be developed.

The work conducted on homogeneous charge compression ignition (HCCI) systems and its challenges are well documented. But engineers are also looking at mixing gasoline systems, direct-injection and compression-ignition systems to make further efficiency improvements.

Delphi has been developing gasoline direct-injection compression-ignition (GDCI) technology for the past six years, and is now in the second phase of its programme.

“As lower and lower emissions are needed around the world, we think this could be a very good engine technology,” says Dr John Kirwan, chief scientist at Delphi.

“For the last six years, under a structured programme funded by the US Department of Energy, we’ve reached a point where we have an operating vehicle and we’re on the path to refining the technology.”

As with HCCI, the system mixes gasoline and diesel technology, but unlike traditional HCCI systems it uses direct injection to better control the combustion process.

As with a diesel engine, the compression ratio is high, there is no intake throttling, and the mixture is lean. GDCI uses a low-temperature combustion process for partially premixed compression ignition. Multiple late injections of gasoline vaporise and mix very quickly.

tags: May 2016 Powertrain