• Energy Research

<div class="section abstract"><div class="htmlview paragraph">The introduction of new light-duty vehicle emission limits to comply under real driving conditions (RDE) is pushing the diesel engine manufacturers to identify and improve the technologies and strategies for further emission reduction. The latest technology advancements on the after-treatment systems have permitted to achieve very low emission conformity factors over the RDE, and therefore, the biggest challenge of the diesel engine development is maintaining its competitiveness in the trade-off “CO₂-system cost” in comparison to other propulsion systems. In this regard, diesel engines can continue to play an important role, in the short-medium term, to enable cost-effective compliance of CO₂-fleet emission targets, either in conventional or hybrid propulsion systems configuration. This is especially true for large-size cars, SUVs and light commercial vehicles.</div><div class="htmlview paragraph">In this framework, a comprehensive approach covering the whole powertrain is of primary importance in order to simultaneously meet the performance, efficiency, noise and emission targets, and therefore, further development of the combustion system design and injection system represent important levers for additional improvements. For this purpose, a dedicated 0.5 dm³ single-cylinder engine has been developed and equipped with, a state-of-the-art Euro 6 combustion system, and an advanced common rail fuel injection system (FIS) offering higher flexibility in terms of injection strategy and higher quantity accuracy. Three injector nozzles with different hydraulic flow rates (HF) have been selected and employed for the overall combustion process optimization.</div><div class="htmlview paragraph">The optimization has been performed by means of an extensive DoE-based test campaign in which the engine and FIS operating parameters have been parametrized with the aim to carry out a proper combination in terms of HF and injection strategy. The results at partial load conditions evidence significant advantages in applying an advanced injection pattern, while the HF reduction can significantly improve the smoke emission and combustion noise without fuel consumption penalties. Therefore, a proper combination and optimization of the HF and injection strategy can provide low noise and engine-out smoke while maintaining the rated power performance targets.</div></div>

Studies consider the influence of biofuels on the decarbonization of the transport system not negligible. The employment of fossil fuels with an even higher degree of renewable biofuel content, produced with a mature technology process, such as the Hydrotreated Vegetable Oils (HVO), are expected to increase. The research community expects valuable research results to exploit the HVO characteristics in ultra-low emission vehicles equipped with internal combustion engines. In this context, new findings in setting combustion control parameters through proper experimental design are carried out on a modern internal combustion engine architecture. An advanced injection system capable of precise close-coupled multiple injections per cycle was utilized. Steady-state engine operating conditions were selected for this experimental study. Combustion, efficiency, and engine-out emissions indicators with HVO fuel are compared with standard diesel. For assessing the difference in combustion stages, a second derivative method data analysis was performed. It is found that in comparison to diesel fuel, HVO significantly reduces regulated engine-out emissions at the same efficiency and EU 6c NOx emissions targets. To this aim, a specific set of engine control parameters were adopted. The PM decreased up to 10 %, corresponding to 0.18 g/kWh, while the CO reduced by about 7-8% in the range of 0.2-0.5 g/kWh. The decrease of the total PN ranges between 10 and 55%, depending on the control strategy and test point, and the particle distribution shifts towards smaller particle sizes. Outstanding improvements of the NOx-soot trade-off are verified, which in turn demonstrates the capability to operate the engine at post-EU6 NOx conditions without performance and comfort penalties. Engine-out CO and HC emission reductions are confirmed.

A wider use of biofuels in internal combustion engines could reduce the emissions of pollutants and greenhouse gases from the transport sector. In particular, due to stringent emission regulatory programs, compression ignition engine requires interventions aimed at reducing their polluting emissions. Ethanol, a low carbon fuel generally produced from biomass, is a promising alternative fuel applicable in compression ignition engines to reduce CO2 and soot emissions. In this paper, the application of a dual fuel diesel-ethanol configuration in a light-duty compression ignition engine has been numerically investigated. Ethanol is injected into the intake port, while diesel fuel is directly injected into the combustion chamber of the analyzed engine. CFD simulations have been carried out by means of the AVL Fire 3-D code. The operation at given engine load and speed has been simulated considering different diesel injection timings. Numerical results of both the diesel spray development and the dual fuel combustion process have been validated against available experimental data. 3-D analysis allowed to deeply investigate the evolution of the combustion process, particularly the transition between premixed and diffusive phase. The influence of diesel fuel direct injection timing, combustion chamber geometry, and EGR on the combustion process development, hence on engine performance and emission levels, have been highlighted. One of the main results of the use of dual fuel, diesel-ethanol configuration, is a significant reduction of soot and carbon dioxide emissions with respect to diesel-only operation.

A viable solution for residual biomass exploitation to reduce the cost related to the biomass disposal and simultaneously create profit by electrical and thermal energy use is combined heat and power generation over the micro-scale of power (m-CHP) based on biomass gasification. The exploitation and improving of these systems were the main objective of the Italian project "PROMETEO - Production of electrical, thermal and cooling energy with m-CHP fueled by residual biomass", funded by the local Ministry of Economic Development (MISE). The present work shows an extended experimental activity based on a 20kW micro-cogeneration system as powered by different types of residual lignocellulosic biomasses briquettes in a demonstrative environment site identified in a waste management and storage plant in the Municipality of Mugnano, Naples, in the south of Italy. The m-CHP plant is made of a gasifier, a syngas cleaning circuit and a spark ignition (SI) internal combustion engine (ICE) connected to an electric-generator. The electrical output was meant to power the plant machines for the operations of waste storage. For both biomasses, tests were conducted over two consecutive days for the complete characterization of the system in low and medium load and in different spark ignition timing to assess the system sensitivity. The plant performance was investigated with a complete characterization of the syngas and tar compositions, main pollutant emissions and internal combustion engine analyses, aimed at the evaluation of the energetic and environmental efficiencies of the whole plant during the exercise. An analysis of the assessment of the air quality near the plant by evaluating CO, O3, NO2, C6H6 and PM10 concentration was also carried out. The ultimate purpose of the present work is the demonstration of the advantages of the employment of biomass-powered cogeneration systems in the Mediterranean regions, as part of biomass-to-energy chains suitable of being set in rural zones, within National Parks as well as to serve Municipalities having the need to dispose green waste from pruning and maintenance operations.

Biofuels represent a viable contribution in increasing the energy system sustainability. Since a long time, ethanol has been used as a fuel for spark-ignition engines and, nowadays, it is being tested also in compression-ignition engines. Furthermore, in order to exploit the emulsifying properties of gasoline, small amounts of this fuel can be added to the ethanol-diesel blends. Due to the presence of bio-mass derived fuels, and considering that ethanol is an oxygenated fuel, this kind of fuel mixtures, fired in high efficiency engines, could lead to the reduction of both CO2 and particulate emissions. In order to deeply investigate the behavior of the above mentioned mixtures, when they are injected at high pressure in the combustion chamber of Diesel engines, numerical analyses have been carried out by using the AVL-FIRE 3-D code. First, the spray characteristics of diesel fuel, injected into a quiescent chamber in non-evaporative conditions, have been numerically evaluated and the obtained results have been compared to the available experimental data. Later, in order to obtain useful information on both the combustion process and the engine emissions, the behavior of the ternary diesel-ethanol-gasoline blend, injected and fired in a Diesel engine available at the test bench, has been numerically simulated. Referring to the simulations of the combustion chamber of the compression-ignition engine, the most remarkable result shows the combustion of oxygenated fuel blends leads to an important reduction of soot production. Furthermore, using diesel-alcohol mixtures, lower NOx emissions have been observed at the analyzed operating points.The original version of this article supplied to AIP Publishing contained an error in the author’s name. The name originally appeared as, G. Di Biasio, but the correct name is G. Di Blasio. An updated version of this article, with the author’s name corrected, was published on 31 March 2020.

The increasing concern of global warming due to the ever-increasing amount of greenhouse gases (GHG) such as carbon dioxide (CO2) and pollutant emissions induces regulatory authorities to stricter emission legislation in the transportation sector. In this context, renewable fuels, such as methanol and ethanol, are considered a promising solution to mitigate the carbon footprint and reduce engine-out emissions. Based on the several studies published in the specific literature, this work aims to summarise and normalize the main outcomes, highlighting the pro and cons of exerting alcohol fuels in compression ignition engines through a critical literature review for helping the researchers, who start to work on these applications. Both dual-fuel and direct-injection fuelling concepts of diesel and alcohol (ethanol and methanol) in compression ignition engines are discussed. Analyses on the combustion, emissions and performance and CO2 are carried out. Depending on the fuel supply method and the engine type, the use of alcohol fuels performs differently in terms of emissions and engine performance. Dual Fuel combustion mode, port fuel injected alcohol, and direct-injected diesel emits higher HC and CO, while diesel-alcohol blends perform as diesel. Generally, the blends characterized by lower alcohol concentration than dual-fuel perform higher indicated thermal efficiencies. Significant benefits on NOx-soot trade-offs are observed, independently on the fuelling mode, NOx concentration, and engine type by using alcohols. The soot reduction reaches values up to 70%, and the lower carbon content of alcohols fuel reduces the CO2 up to 15%.

Carbon dioxide (CO2), nitrogen oxides (NOx) and soot emissions are primary concerns and the most investigated topics in the automotive sector. Indeed, recent governments directives push toward carbon-neutral mobility by 2050. In this framework, zero-carbon fuels, as hydrogen, or renewable low carbon alcohol fuels, play a fundamental role. To this aim, in this chapter, the main results on largely used alcohol fuels application in spark-ignition (SI) engines are discussed. Aspects inherent ethanol and methanol production processes, chemical-physical properties and their application in SI engines are presented. Different engine fuelling strategies, dual fuel and blend are analysed. Alcohols have higher enthalpies of vaporisation and research octane number (RON) values as well as excellent anti-knock ability compared to gasoline. This effect enhances in dual fuel mode. Ethanol and methanol have higher thermodynamic conversion efficiencies than gasoline combustion. Cycle to cycle variation is in line with gasoline values. In general, NOx decreases with alcohol fuels, and the best results are achieved in blend mode with a reduction of up to 30% with methanol compared to gasoline. Independently of the fuelling mode, significant benefits on particle number emissions are observed by using alcohol fuels. Carbon monoxide (CO) and hydrocarbons (HC) emission trends strongly depend on fuelling mode and engine operating conditions. Additionally, the lower carbon content of alcohol fuels reduces the CO2 emissions up to 10% compared to reference gasoline.

Compression ignition (CI) engines are widely used in modern society, but they are also recognized as a significative source of harmful and human hazard emissions such as particulate matter (PM) and nitrogen oxides (NOx). Moreover, the combustion of fossil fuels is related to the growing amount of greenhouse gas (GHG) emissions, such as carbon dioxide (CO2). Stringent emission regulatory programs, the transition to cleaner and more advanced powertrains and the use of lower carbon fuels are driving forces for the improvement of diesel engines in terms of overall efficiency and engine-out emissions. Ethanol, a light alcohol and lower carbon fuel, is a promising alternative fuel applicable in the dual-fuel (DF) combustion mode to mitigate CO2 and also engine-out PM emissions. In this context, this work aims to assess the maximum fuel substitution ratio (FSR) and the impact on CO2 and PM emissions of different nozzle holes number injectors, 7 and 9, in the DF operating mode. The analysis was conducted within engine working constraints and considered the influence on maximum FSR of calibration parameters, such as combustion phasing, rail pressure, injection pattern and exhaust gas recirculation (EGR). The experimental tests were carried out on a single-cylinder light-duty CI engine with ethanol introduced via port fuel injection (PFI) and direct injection of diesel in two operating points, 1500 and 2000 rpm and at 5 and 8 bar of brake mean effective pressure (BMEP), respectively. Noise and the coefficient of variation in indicated mean effective pressure (COVIMEP) limits have been chosen as practical constraints. In particular, the experimental analysis assesses for each parameter or their combination the highest ethanol fraction that can be injected. To discriminate the effect on ethanol fraction and the combustion process of each parameter, a one-at-a-time-factor approach was used. The results show that, in both operating points, the EGR reduces the maximum ethanol fraction injectable; nevertheless, the ethanol addition leads to outstanding improvement in terms of engine-out PM. The adoption of a 9 hole diesel injector, for lower load, allows reaching a higher fraction of ethanol in all test conditions with an improvement in combustion noise, on average 3 dBA, while near-zero PM emissions and a reduction can be noticed, on the average of 1 g/kWh, and CO2 compared with the fewer nozzle holes case. Increasing the load insensitivity to different holes number was observed.