Sellnau, M., Foster, M., Moore, W., Sinnamon, J. et al., "Second Generation GDCI Multi-Cylinder Engine for High Fuel Efficiency and US Tier 3 Emissions," SAE Int. J. Engines 9(2):1002-1020, 2016, doi:10.4271/2016-01-0760.
The second generation 1.8L Gasoline Direct Injection Compression Ignition (GDCI) engine was built and tested using RON91 gasoline. The engine is intended to meet stringent US Tier 3 emissions standards with diesel-like fuel efficiency. The engine utilizes a fulltime, partially premixed combustion process without combustion mode switching.The second generation engine features a pentroof combustion chamber, 400 bar central-mounted injector, 15:1 compression ratio, and low swirl and squish. Improvements were made to all engine subsystems including fuel injection, valve train, thermal management, piston and ring pack, lubrication, EGR, boost, and aftertreatment. Low firing friction was a major engine design objective.Preliminary test results indicated good improvement in brake specific fuel consumption (BSFC) over the first generation GDCI engines, while meeting targets for engine out emissions, combustion noise and stability. BSFC at the 2000 RPM-2 bar BMEP global test point was 248 g/kWh. At 1500 RPM, low BSFC of 210 to 215 g/kWh was measured over a wide load range from 6 to 12 bar BMEP. Friction levels were reduced considerably over Gen 1 engine friction. Tests at 800 RPM idle with zero brake torque indicated very stable combustion with very low NOx and PM emissions.Initial warmed up tailpipe CO emissions were very low with good potential to meet US Tier 3 targets. Tailpipe non-methane HC were also low at low to medium loads, but increased at higher loads. Improved HC aftertreatment will be needed for Tier 3 targets. NOx aftertreatment was not used on this engine but is expected to be needed for Tier 3-Bin 30 emissions standards.A detailed thermodynamic loss analysis was performed at various operating conditions. Indicated thermal efficiency was high due to low heat losses and an efficient combustion process. A mechanical loss analysis was also performed. While firing friction was low, boost parasitics were significant at higher loads. Reduction of boost parasitics is an opportunity for further brake efficiency improvements.