Heavy-duty diesel vehicles are a significant source of nitrogen oxides (NOx) in the atmosphere. The Selective Catalytic Reduction (SCR) system is a primary aftertreatment device for reducing NOx emissions from heavy-duty diesel vehicles. With increasingly stringent NOx emission regulations for heavy-duty vehicles in major countries, there is a growing focus on reducing NOx emissions under low exhaust temperature conditions, as well as monitoring the conversion efficiency of the SCR system over its entire lifecycle. By reviewing relevant literature mainly from the past five years, this paper reviews the development trends and related research results of SCR technology, focusing on two main aspects: low-temperature NOx reduction technology and the combination of SCR systems with remote On-Board Diagnostics (OBD). Regarding low-temperature NOx reduction technology, the results of the review indicate that the combination of multiple catalytic shows potential for achieving high conversion efficiency across a wide temperature range; advanced SCR system arrangement can accelerate the increase in exhaust temperature within the SCR system; solid ammonium and gaseous reductants can effectively address the issue of urea not being able to be injected under low-temperature exhaust conditions. As for the combination of SCR systems with remote OBD, remote OBD can accurately assess NOx emissions from heavy-duty vehicles, but it needs algorithms to correct data and match the emission testing process required by regulations. Remote OBD systems are crucial for detecting SCR tampering, but algorithms must be developed to balance accuracy with computational efficiency. This review provides updated information on the current research status and development directions in SCR technologies, offering valuable insights for future research into advanced SCR systems.

General aviation (GA) aircraft generally driven by aviation piston engines (APE) are currently experiencing promising growth globally. To relieve the fossil fuel scarce, the application of alternative fuels was extensively encouraged for green GA development. This study aims to investigate the suitability of using aviation kerosene rocket propellant 3 (RP-3) and its pentanol blends (by 30% volume fraction) in an aviation compression ignition (CI) engine, by comparing their combustion performance and emission characteristics differences under various injection timings with baseline diesel. The major combustion parameters including the in-cylinder pressure, heat release rate, ignition delay, combustion duration, indicated thermal efficiency (ITE), and indicated specific fuel consumption (ISFC) were evaluated as the crank angle (CA) 50 swept from 9 to 15° crank angle after top dead center (ATDC). The ITE of RP-3/Pentanol blends presented to be higher than those of diesel by 4.2%−5.0%, and pure RP-3 by 2.6%−3.4%. The improved ITE of the blended fuel is due to the longest ignition delay and the shortest combustion duration under all the CA50. Moreover, the particulate matter (PM) emissions with the number concentration, geometric mean diameter (GMD), size-resolved distribution characteristics were quantitatively analyzed for all the test fuels. RP-3/Pentanol dramatically reduced the number-based PM, by over 50% and two magnitudes of order lower than those of RP-3 and diesel, respectively. Improved PM emissions from the alcohol blends intensively was caused by the better premixing and evaporating states with subsequent homogeneous combustion. Additionally, the PM emissions of the three fuels exhibited different sensitivities to the varied injection timings. With the retardance of injection timings, the PM declined apparently for diesel and RP-3 due to prolonged ignition delay and decreased in-cylinder temperature, but remained nearly unchanged for RP-3/Pentanol because of the growth of nucleation mode PM.