The era of personnel mobility is entering a period of deep evolution: in the next decade, the well-established matchup between conventional engines and oil derived fuels will rapidly move towards new powertrain architectures for electric-hybrid and full electric solutions. But it will also include more and more alternative low carbon fuels, progressively integrating the contribution from advanced bio- and renewable fuels.
The need in accelerating the decarbonization process and in increasing air quality, especially in large urban agglomerations, will leverage on the right combination of vehicle efficiency and fuel properties.
With the progressive swift from a prominent Diesel based European market to a gasoline based one, essentially due to the complexity of the Diesel after-treatment system and to the need in optimizing the powertrain cost for hybrid applications, natural and renewable gas will have an important role to play.
Thanks to its “natural” characteristics, and particularly to the high knocking resistance (equivalent RON = 130 for CH4), compressed natural gas (CNG) is an excellent fuel for highly efficient engines, combining downsizing, high compression ratio and boosting, and dedicated valvetrain optimization.
Today, natural gas is offering already a 23-24% tailpipe (‘Tank-to-Wheel’) CO2 emissions reduction compared to gasoline, and between 6% and 9% according to Diesel engine efficiencies. Considering also the so called ‘Well-to-Tank’ contribution (related to fuel production and distribution) the benefits on a ‘Well-to-Wheel’ are similar to tailpipe ones, as illustrated in the figure below (Thinkstep study – May 2017 – www.ngvemissionsstudy.eu).
The emissions shown in the visual are calculated as CO2 equivalent which means already including the contribution from CH4 and N2O emissions.
Today, natural gas is providing a tailpipe CO2 emissions reduction that is comparable to the one obtained with a gasoline hybrid high voltage system (HEV). But the effect from the fuel composition ensures a constant gain in CO2 emissions reduction independently from the operating conditions: under steady state conditions, like during a highway trip, a HEV system cannot provide any substantial contribution, while the low carbon content of natural gas always translates into a 23-24% gain over gasoline.
Future evolution of CNG dedicated engines is today focusing on the development and implementation of new direct injection gas system that, in combination with other engine technologies, will further improve the engine efficiency. The Horizon 2020 project GASON (www.gason.eu) is demonstrating the technical feasibility to improve current state of the art CNG engine efficiency by 10-12%. This will mean to be able to combine highly efficient CNG dedicated engines also in hybrid powertrain architectures, mainly mild-hybrid (MHEV) and hybrid (HEV), matching the benefits coming from both solutions.
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