It is evident that a novel engineering solution is required in order to elevate a greater number of polluting cars into a higher category. There appears to be a paucity of direct interest in upgrading Euro 1, 2, 3, 4, and 5 vehicles to the highest possible level, primarily through software modifications of the parameters determining the performance of the internal combustion engine (ICE). The potential for advancement in this area is evidenced by the presence of systems that enhance environmental efficiency, even in Euro 2 vehicles. These include exhaust gas recirculation, catalytic converter, lambda sensor, electronic control fuel injection, and ignition timing. It is precisely these vehicles that are subject to optimization, a process which would allow the maximum service life of otherwise more reliable but older vehicles to be exploited.

This study investigates the relationship between exhaust gas composition, particle number (PN) emissions, and soot microstructure of a 1.9 L compression-ignition engine operated under six controlled steady-state load regimes at 2000 min⁻¹. Unlike standardized transient procedures (e.g., WLTP), the steady-state approach enables isolation and quantification of fundamental thermochemical processes governing soot formation and NO_x production, providing engine-out data highly relevant for understanding Euro 7 emission behavior at the source. The novel contributions of this study include (i) a combined macroscopic–microscopic analysis linking PN emissions with SEM/EDS-based soot morphology; (ii) distribution-based estimation of soot mass concentration using experimentally derived primary particle sizes; and (iii) an experimental demonstration of the NO_x–soot trade-off across increasing load, supported by microstructural evidence of soot oxidation and agglomeration. The results show a clear decrease in PN concentrations with increasing load (from 1.31 × 10⁷ to 6.4 × 10⁶ cm⁻³), accompanied by a marked rise in NO_x emissions and exhaust temperature. SEM analysis confirms a transition from fine, weakly agglomerated soot structures at low load to more compact, oxidized aggregates at high load. Distribution-based particle sizing (20–80 nm, average ~45 nm) yields soot mass estimates that are consistent with theoretical trends and more accurate than fixed-radius approaches. These findings provide experimentally supported insights into engine-out particulate behavior that complements regulatory PN metrics in Euro 7, offering a mechanistic basis for improved emission control strategies and for interpreting PN-focused regulatory thresholds under real-world operating conditions.

This study presents a single-case multi-sensor experimental study of thermal loading and emission variation in a high-mileage gasoline engine operating at idle under deliberately impaired cooling until mechanical failure. A production vehicle equipped with a naturally aspirated gasoline engine with a displacement of 1600 cc was operated under relatively steady-state conditions at idle, while gaseous emissions (CO, CO₂, HC, NO_x, and O₂), air–fuel ratio λ, particle number (PN), oil temperature, infrared thermal indicators, and acoustic performance variation were continuously monitored. The results are interpreted primarily in terms of their dependence on the engine oil temperature. They show that despite stable conditions of the air–fuel ratio and an almost constant amount of residual oxygen in the exhaust gases, progressive thermal loading leads to pronounced changes in the behavior of the emissions emitted by the engine during its operation. Hydrocarbon emissions show increased variability and escalation at elevated engine oil temperatures, while nitrogen oxides show a strong temperature-dependent increase, consistent with thermally driven formation mechanisms. The most significant response is observed in the particle number (PN) emissions, which go from low and stable levels to a rapid, multi-step increase in a narrow temperature range preceding mechanical failure. Under the tested cooling impairment scenario, emission behavior was dominated by cumulative thermal stress rather than mixture composition effects. In the investigated case, particle number emissions emerged as a sensitive indicator of system-level thermal instability. The findings provide experimentally documented insight into the system-level progression toward thermal runaway under impaired cooling conditions and its measurable impact on emission behavior in the tested engine.

Thermal overload in internal combustion engines may progressively destabilize lubricant-film integrity and promote severe tribological deterioration within highly stressed contact interfaces. This study investigates the thermo-tribological degradation sequence of a high-mileage gasoline engine subjected to prolonged idle operation under impaired cooling conditions, ultimately resulting in engine seizure. The investigated engine had accumulated 356,724 km, while the lubricant had remained in service for approximately 26,724 km prior to the experiment. The post-failure investigation combined teardown inspection, geometrical camshaft assessment, reverse gravimetric reconstruction, hydraulic tappet surface profiling, XRF surface characterization, laboratory oil analysis, and SEM/EDS evaluation of wear debris. The results demonstrated strongly localized degradation concentrated primarily within the cam–tappet interfaces. Severe non-uniform camshaft wear was accompanied by pronounced hydraulic tappet surface damage and evidence of unstable boundary-lubrication conditions. Laboratory oil analysis revealed elevated wear-metal concentrations, depletion of the alkaline reserve, increased oxidation indicators, and a final Class D oil condition assessment. SEM/EDS characterization identified Fe-bearing wear debris associated with sustained material removal and debris recirculation during the final degradation stage. The combined evidence supports a coupled thermo-tribological degradation mechanism involving lubricant deterioration, boundary-lubrication instability, adhesive wear acceleration, oxidative surface degradation, and debris-assisted surface damage preceding final engine seizure. The present case study provides experimentally documented evidence of lubrication collapse under real-engine thermal runaway conditions and highlights the critical role of lubricant condition in maintaining tribological stability under severe thermal loading.

The development of internal combustion engines aims to maximize the combustion process energy, achieve the highest possible efficiency, and reduce harmful emissions released into the environment, while also improving power output. In this regard, here we have presented two pairs of vehicles which have mechanically similar internal combustion engines but either different environmental or dynamic performance characteristics. The first example is of upgrading an internal combustion engine from Euro 4 to Euro 5. The second example demonstrates a 23% increase in power while maintaining the same emission parameters.