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Review of Vehicle Engine Efficiency and Emissions
Abstract:
This review covers some of the major advances pertaining to reducing tailpipe emissions of greenhouse gases and criteria pollutants. Discussed are both new and upcoming regulations, and technologies being developed for improving engines and after-treatment systems.
There is clearly a focus on reducing greenhouse gas emissions in major countries, implemented through ambitious CO2 and electrification targets. Several mature IC engine (ICE) technologies are reviewed which promise to deliver double digit reductions in CO2 emissions. We cover some of these in detail, including gasoline compression ignition, pre-chamber combustion, water injection, and cylinder deactivation. Electrification of the powertrain and synergistic gains with advanced engine technologies are examined. The case is made for the need for cradle-to-grave analyses when evaluating various powertrain choices, and highlight the role hybrids can play in achieving significant and immediate CO2 reductions. For the first time, also briefly discussed are the role of advanced fuels and their potential for improving emissions.
On criteria pollutants, the focus remains on reducing NOx and particulates. California is leading the charge on an omnibus rulemaking for heavy-duty trucks, targeting a 90% reduction in NOx emissions, and elements of the proposal are discussed. The challenge is to achieve this reduction without affecting CO2 emissions. Various studies are underway and technological pathways are being proposed and we cover the leading concepts. These include close-coupled SCR with dual dosing, innovative solutions for low temperature urea dosing, cylinder deactivation, advanced combustion techniques, electrification and natural gas engines.
For light-duty vehicles, real-world driving emission (RDE) norms seem to be addressing the discrepancy between lab and on-road NOx emissions, and the relevant data are discussed. Discussions are ongoing for post Euro-6 light duty regulations, and both the possible regulatory changes as well as after-treatment system developments are covered. A major focus will remain on reducing cold-start emissions and studies for both diesel and gasoline engines are reviewed.
Particle number standards in Europe and China have enforced gasoline particulate filters (GPFs) in those markets, and improvements in that technology are summarized. Filtration efficiency requirements are expected to increase with further tightening of regulations, and GPFs are also expected to be required for port fuel injected vehicles in the future.