Researchers from Saudi Aramco and KAUST (King Abdullah University of Science and Technology), with a colleague from Shanghai Jiao Tong University in China, assessed the effects of adopting 4 hybrid architectures on the life-cycle GHG emissions of a novel high-reactivity fuel in an advanced compression-ignition engine (GCI). Their paper appears in the journal Applied Energy.

They contrasted 4 hybrids against conventional fuels/engines and a comparable battery electric vehicle using regionally-explicit power mixes in the 3 biggest automotive markets worldwide (China, US and Europe).

WTW GHG reduction ranges afforded by the different GCI hybrid architectures. Abdul-Manan et al.

At a high level, they found that:

• Gasoline Compression-Ignition (GCI) hybrids reduce WTW GHG emissions by 7–43% versus unhybridized GCI.

• GCI hybrids reduce WTW GHG emissions by 26–55% versus conventional SI.

• WTW GHG reduction for BEV depends on the availability of cleaner power.

• The use of larger batteries enabled higher degrees of electrification with potentially lower overall emissions. However, they found diminishing returns for every kWh of increasing battery size: a mild hybrid resulted in more than 50% GHG reduction per kWh of battery, whereas an electric vehicle only reduced emission by 4% per kWh given its much larger battery requirement.

The effectiveness of every kg of lithium (left) and cobalt (right) in reducing the WTW GHG emissions of a passenger car reduces with increasing battery size. The WTW GHG emissions reductions were calculated relative to conventional SI engine. Abdul-Manan et al.

For the study, the team used a typical medium-sized European C-segment passenger car that is equipped with a GCI engine platform, and capable of achieving 95 gCO₂/km, consistent with the EU requirements for 2021.

GCI engines combine the benefits of diesel compression-ignition and gasoline spark-ignition; unlike a diesel compression-ignition engine, a GCI engine can operate with a lower-reactivity fuel for better fuel mixing time and thereby produce lower emissions of NO_x and particulates.

They used four hybrid architectures in their evaluation:

• 48V mild hybrid (P0 & P2)
• Parallel hybrid (full hybrid)
• Series hybrid (full hybrid)
• Parallel/series 2-mode hybrid (full hybrid)

Four reference vehicles were equipped with:

• gasoline spark-ignition (SI) engine
• diesel compression ignition (CI) engine
• non-hybridized GCI engine running on a new high-reactivity fuel, and
• fully electrified battery electric vehicle (BEV)

Resources

• Amir F.N. Abdul-Manan, Hyun-Woo Won, Yang Li, S. Mani Sarathy, Xiaomin Xie, Amer A. Amer (2020) “Bridging the gap in a resource and climate-constrained world with advanced gasoline compression-ignition hybrids,” Applied Energy, Volume 267 doi: 10.1016/j.apenergy.2020.114936