• Energy Research

Abstract Downsizing with turbocharging is the most promising way, especially in terms of cost, to get reduced fuel consumption and CO 2 emissions particularly in the case of Spark Ignition engines. In automotive applications the turbocharger turbine usually operates under heavy unsteady flow conditions due to the opening and closing of engine valves. However, in the case of extremely downsized engines with a reduced number of cylinders and a small intake circuit volume also the compressor performance can be affected by the unsteady flow generated by the engine intake valves. To make simulation models able to accurately predict engine performance, a better understanding of compressor and turbine pulsating flow performance can be accomplished through measurements performed on specialized test facilities, using suitable measuring equipment. As regards the turbocharger compressor, the surge line position under pulsating flow conditions is another important aspect to be considered. In the paper the results of a broad experimental investigation performed on a small turbocharger compressor matched to a downsized gasoline engine are presented. Measurements were developed on the test facility operating at the University of Genoa, which allows investigations on automotive turbochargers both under steady and unsteady flow conditions. Tested turbocharger compressor was coupled to the automotive engine intake circuit and the pulsating flow was generated by a motor-driven cylinder head fitted with a variable valve actuation system. Different levels of turbocharger rotational speed and different intake valve opening strategies were considered. For each operating condition compressor unsteady performance was evaluated starting from measurement of several instantaneous parameters (inlet and outlet static pressure, mass flow rate and turbocharger rotational speed). A significant deviation of compressor instantaneous performance from steady state was observed, resulting in a hysteresis loop surrounding the steady state curve.

Regulated pollutant emissions and fuel consumption were characterized at the exhaust of two Euro 3 4-stroke medium-size motorcycles during the execution of both standard and real world driving cycles. A principal component analysis was carried out to group in a cluster the driving cycles with similar kinematic parameters. Hot start results, analysed according to this cluster grouping, show that the main differences are explained by overall mean speed and high positive acceleration of driving cycles. Lower mean speeds produce higher CO2 emission factors, while the influence on CO and HC is more complex. NOX are not significantly affected by the driving pattern. Inside the same cluster, the whole duration of the acceleration phases could discriminate emission behaviour. In-depth analysis of cold start results was conducted in order to assess the influence of the driving cycle and vehicle characteristics on cold start duration. Cold start extra emissions are more influenced by the duration of the enrichment phase than by the catalyst light-off. The larger number of accelerations occurring during real world driving cycles produces higher variability of air fuel ratio and hence higher cold start extra emissions.

An experimental investigation was performed with a view to comparing high and low pressure exhaust gas recirculation systems (HP and LP EGR) fitted on an automotive turbocharged diesel engine, focusing on analysing their influence on fuel consumption, pollutant emissions and the combustion process. Following the development of a prototype cooled LP EGR circuit, the main engine and turbocharger parameters were measured in six part-load operating conditions related to the European driving cycles. Different operating modes were considered, from the simplest and most commonly investigated (without EGR, with HP or LP EGR) to more complex schemes, namely the simultaneous application of high and low pressure recirculation and the addition of variable nozzle turbine (VNT) control. The extensive experimental database made it possible to confirm literature concerning the comparison of recirculating systems and the potential of LP EGR on engine intake temperature and NOx reductions. New aspects were also analysed, such as the balance of the high and low pressure EGR rate in order to achieve maximum NOx reductions in simultaneous applications, the interactions between EGR circuit management and the application of VNT control in order to improve the trade-off between fuel consumption and NOx and soot emissions.

Abstract An experimental investigation was made on a downsized Euro 5 turbocharged diesel engine managing high/low pressure EGR systems and the variable nozzle turbine, aiming at major reductions in NOX emissions while enhancing fuel consumption in comparison with reference configuration. Three part load engine operating conditions were chosen at low and medium speed levels, applying different strategies to a number of control variables (relative air–fuel ratio, VNT opening degree/intake pressure, valves position in low pressure EGR circuit), thus exploring the whole range of high/low pressure EGR proportion. In suitable operating modes of tested conditions, NOX emissions were reduced up to 58–66%. Brake specific fuel consumption decreased around 5–9.5% at low speed/load, 1.7–3.3% in the intermediate condition while no advantages were achieved in the third working point. The activation of low pressure loop confirmed to be beneficial for turbocharger performance, rising its rotational speed thus granting for a better transient response, while increase in soot emissions ranged in a wide interval. For each condition, optimal operating modes were identified, with the relevant EGR proportion. A prevailing contribution from the long route circuit was generally requested, up to the exclusion of short route loop at higher level of speed and load.

Abstract An experimental and theoretical investigation is being performed to evaluate exhaust emissions and fuel consumption of Heavy Duty Vehicles (HDVs) circulating in urban areas and involved in commercial shipping activities. The study is focused on the city of Genoa, whose urban road network is influenced by highway connections and shipping activities, as seven motorway exits and more than twenty accesses to port area are located within the urban area. In a first step, the HDV flows crossing highway exits, urban zones and port areas were evaluated, as well as the relevant vehicle classes. The typical urban trips linking highway exits to port gates and the HDV mission profiles within the port area were then defined, whose validation was performed through an experimental campaign for HDV instantaneous speed measurements on urban trips and in port zones. The availability of speed patterns enabled the application of Passenger Car and Heavy Duty Emission Model (PHEM) for the estimation of fuel consumption and emission factors for selected HDV classes. The main results of the different investigation steps are presented and discussed in the paper, outlining the specific activities of HDVs in port area and the relevant emissive behaviour.

Abstract An experimental investigation on instantaneous speed measurements with instrumented motorcycles was performed considering three typical urban trips, divided in twelve sections according to different road classes. The main kinematic parameters obtained by processing experimental values are presented and compared with those referred to standard cycles, confirming that real world driving conditions are hardly reproduced by statutory cycles. Several applications of measured data are then analysed. Exhaust emission and fuel consumption factors were calculated for different motorcycle classes by applying the functions of Copert, Artemis and Progress models and the Artemis traffic situation approach, considering typical average speed levels and the experimental values. Results are then compared in order to highlight the differences between applied functions and methodologies. A selection of speed profiles was also performed in order to define the emissive behaviour of two-wheelers on the chassis dynamometer: experimental emission and consumption factors for a Euro 3 scooter are related to calculated levels, while measured cold and hot exhaust emissions and fuel consumption of a Euro 2 moped are compared with the results obtained on standard and real world driving cycles, proving that the new speed patterns may be useful to define emissions and fuel consumption of these vehicles.

Abstract To make simulation models able to accurately predict engine performance, a better understanding of compressor behavior over an extended range can be accomplished by using a specialized test facility and measuring equipment. Besides, the correct surge line position is another important aspect to be considered to optimize engine-turbocharger matching calculation. In the paper the results of an experimental investigation developed on a turbocharger compressor for heavy duty vehicle application is presented. The study was focused on the definition of surge line position adopting different methods and on the evaluation of compressor performance over an extended range, taking into account compressor behavior both in the stable and unstable operating region.

A wide experimental campaign was developed on an automotive turbocharged diesel engine, using two blends between diesel oil and waste cooking oil methyl esters (WCOME) and neat biodiesel. A conventional B7 diesel oil was considered as reference fuel. The two blends respectively included 40 and 70% of WCOME, on a volumetric basis. The influence of biodiesel was analyzed testing the engine in two part load operating conditions, applying proper control strategies to the exhaust gas recirculation (EGR) circuit and rail pressure, in order to assess the interactions between the engine management and the tested fuels. Variable nozzle turbine (VNT) was controlled to obtain constant level of intake pressure in the two experimental points. Referring to biodiesel effects at constant operating mode, higher WCOME content generally resulted in better efficiency and soot emission, while NOX emission was negatively affected. EGR activation allowed for limited NO formation but with penalties in soot emission. Furthermore, interactions between EGR circuit and turbocharger operations and control led to higher fuel consumption and lower efficiency. Finally, the increase of rail pressure corresponded to better soot emission and penalties in NOX emission. Combining all these effects, the selection of EGR rate and rail pressure values higher than the standard levels resulted in better efficiency, NOX and soot emissions when comparing blends and neat biodiesel to conventional B7, granting for advantages not only referred to Green House Gas emissions. Combustion parameters were also assessed, showing that combustion stability and combustion noise were not negatively affected by biodiesel use. Combustion duration was reduced when using WCOME and its blend, even if centre of combustion was slightly shifted along the expansion stroke.

The shipping sector is required to give a significant contribution to the reduction of Green House Gas (GHG) emissions, according to the ambitious goals fixed by the International Maritime Organization (IMO). To achieve these targets, new technologies and measures are required, related to logistics, digitalization, hydrodynamics, machinery, energy, and aftertreatment. A large potential to reduce GHG emissions is offered by alternative fuels. In this perspective a Well-to-Wake (WtW) approach is due for a comprehensive analysis. The paper is focused on the evaluation of WtW CO2 equivalent emission factors for LNG, methanol, and ammonia. The extensive bibliographic research on this topic outlines the large differences occurring when considering grey or green fuel production pathways. A case study based on a cruise ship allows to compare alternative fuels produced from fossil or renewable sources, considering two typical cruise profiles. Results in terms of Carbon Intensity Indicator confirms that the WtW approach points out the great potential of alternative green fuels for GHG emissions reduction.