Delphi Powertrain Study Concludes 3-Cylinder Turbo Gasoline Direct Injection Engine Offers a High-Value NOx and CO2 Solution for Cost-Sensitive Vehicle Segments

. The use of turbocharging and gasoline direct injection contribute to the delivery of sufficient torque across the engine and particularly at lower speeds in the downsized/downspeeded scenario. GDI operates in both homogeneous and lean stratified engine
configurations.

Stoichiometric operation with homogeneous GDi allows the use of conventional 3-way
exhaust catalysts and thus worldwide application without
concerns for lean NO_x production and aftertreatment.

Downsizing can be accomplished via reduction in the number of cylinders, and/or a reduction in the displaced volume of each cylinder. Delphi began its value analysis with a 1.6L naturally-aspirated baseline vehicle and evaluated the benefit of 25% (modest)
downsizing to 1.2L turbocharged engines with downspeeding, looking at 4-cylinder naturally aspirated configurations versus downsized turbocharged 3-cylinder applications.

Overall, Delphi favors a 3-cylinder configuration as opposed to a 4-cylinder for reduced fuel consumption and regulated emissions for a number of factors, including better high load scavenging for high load performance. A 3-cylinder engine also offers cost and packaging advantages and provides acceptable NVH with counterbalancing. Delphi concluded that 3-cylinder turbocharged engines are attractive for engines up to 1.5 L displacement.

In its value analysis, Delphi found that for a compact vehicle
meeting Euro 4 standards, a 4-cylinder turbo-Diesel reduces
CO₂ emissions at an on cost rate of €22 / percent CO₂
reduction.

Our analysis of compact turbocharged vehicles configured to meet Euro 6 emissions in 2014 shows two gasoline configurations and one Diesel powertrain
mechanization to have the best value. They reduce CO₂ at an
on cost rate of 24-25 euros / percent. The turbo-Diesel configuration is a downsized 3-cylinder engine with engine-out NO_x that must be capable of meeting the Euro 6 NO_x standard without lean aftertreatment. Both preferred
turbocharged GDi applications are 3-cylinder stoichiometric engines with conventional three-way catalytic converters.

The turbocharged 3-cylinder stoichiometric GDi powertrains we considered noticeably reduce the CO₂ emissions difference between gasoline and Diesel powertrains. And the
stoichiometric GDi solutions have substantially lower cost, a factor that can be particularly important for lower-priced vehicles. The turbocharged 3-cylinder stoichiometric GDi solutions also employ a traditional 3-way catalytic converter
to meet the most stringent NO_x emissions regulations such as the US Tier 2 standards and future standards being postulated for Euro 6+. Thus turbocharged 3-cylinder stoichiometric GDi powertrains offer a robust method to reduce CO₂ with
low NO_x for worldwide application in the compact vehicle
segment.

—Kirwan et al.

Resources

• John E. Kirwan, Mark Shost, Gregory Roth and James Zizelman (2010) 3-Cylinder Turbocharged Gasoline Direct Injection: A High Value Solution for Low CO₂ and NO_x
  Emissions (SAE 2010-01-0590)