The impact of Euro 4 compression ignition engines over the air quality in Europe has been analyzed in this work by comparing them with Euro 6d emissions regulation. The Euro 6d diesel engine has been chosen as the preferred replacement according to its advantages in global warming potential (GWP) emissions, like methane hydrocarbons (MHC) and CO₂, with respect to Euro 6d petrol-based powertrains. The motivation for this study is that the effects of the emissions reduction policies, as the implementation of the regulation Euro 6d, are necessarily limited due to the great number of passenger cars still in circulation that were homologated under Euro 4 or older standards. To address the impact of the old vehicle pool, a Worldwide harmonized Light-vehicles Test Cycle (WLTC) has been used to analyze the performance and pollutant emissions of a Euro 4 diesel engine in altitude conditions. This driving cycle and engine are considered as a baseline for the subsequent discussion, where the altitude plays a key role because of the European geography. It forces passenger cars to drive over sea level during a significant number of trips. Thus, an analysis of how significant would be the impact of energy policies promoting the substitution of the pre-Euro 5 diesel fleet (>10 years old) by modern Euro 6d engines in the short term on the pollutants and GWP emissions reduction is presented.

According to current worldwide trends for homologation vehicles in real driving conditions is forced to test the engines in altitude and in highly dynamic driving cycles in order to approach nowadays and next future emissions standard. Up to now, there were two main options to perform this type of tests: round-robin tests of the whole vehicle or hypobaric chambers, both with high costs and low repeatability. In this paper a new device is described, which can emulate ambient conditions at whatever altitude between sea level and 5000 m high. Even it can be used to emulate ambient conditions at sea level when test bench is placed up to 2000 m high. The main advantages of the altitude simulation equipment are as follows: dynamic emulation of all the psychrometric variables affecting the vehicles during round-robin tests; lower space usage and low-energy consumption. The altitude simulator (AS) has been validated comparing with results from a hypobaric chamber at different altitudes. Previously a research about the dispersion in the measurements of both testing devices has been done for assessing the results of the comparison experiment. Final conclusion resulted in the same operating performance and emissions of the studied engine with both types of testing equipment for altitude simulation.

In this paper, a procedure for the design of a bubble reactor which allows the control of the humidity of a gas stream used as combustion air is presented. This reactor is designed to be used as a component of an altitude simulator test facility for the optimization, homologation and calibration of new hybrid engines. The design has been carried out by means of Computational Fluid Dynamics (CFD) multi-phase models and validated against the experimental data obtained from the developed prototype. A discussion about the adequate mesh topology and cell size is presented, as well as a comparison between the two available models for the air–water interphase. Lastly, a validation of the CFD results using experimental data shows that the model that should be used is the multi-regime interaction model, from which the final design for the bubble reactor was obtained.