• Energy Research

Compression ratio is one of the main properties of a reciprocating internal combustion engine defined by its geometry. Typical values are between 8 and 12 for Spark Ignition (SI) engines and between 12 to 24 for Compression Ignition (CI) engines. The ignition in engine operating with producer gas takes place via spark and thanks to a higher octane rating compared to gasoline, it is possible to use engine with a higher compression ratio in order to increase the thermal efficiency of the process. To test the behaviors of the producer gas combustion with different compression ratios four engines were used. Two of them were GM Vortec 3 Liters, with 8.3:1 and 10.5:1 compression ratios respectively, in this case the comparison was based on the exhaust emissions and on the maximum electrical power output reached. The other two were Ashok Leyland 3.8 Liters both with compression ratios higher than the GM engines, which were 12:1 and 16:1. This time, the comparison related mostly to the manifold absolute pressure and to the input from a Bosch Knock sensor. Both the Ashok Leyland engine heads were disassembled from the crankcase in order to inspect pistons and combustions chamber. Results obtained with the two GM engines showed higher performances of the 10.5:1 one in terms of maximum power output compared to the 8.3:1, and similar emissions. The test with the two Ashok Leyland showed lower manifold absolute pressure at the same power output for the 16:1 engine, indicating better performances. During the engine inspection no signs of erosion or wear were observed, confirming the input from the knock sensor about the total or near-total detonation absence. Proceedings of the 27th European Biomass Conference and Exhibition, 27-30 May 2019, Lisbon, Portugal, pp. 1927-1931

Abstract A complete mathematical model and software implementation of a solar hydrogen hybrid system has been developed and applied to real data. The mathematical model has been derived from sub-models taken from literature with appropriate modifications and improvements. The model has been implemented as a stand-alone virtual energy system in a model-based, multi-domain software environment. A test run has then been performed on typical residential user data-sets over a year-long period. Results show that the virtual hybrid system can bring about complete grid independence; in particular, hydrogen production balance is positive (+1.25 kg) after a year’s operation with a system efficiency of 7%.

Abstract One of the most innovative solutions concerning CHP for residential and industrial applications consists in using fuel cell devices. The importance of this technology is connected to the possibility of having a nearly complete energetic independence. A comparison between traditional systems for energy generation and co-generative fuel cell systems is needed to properly evaluate whether fuel cells could be a reasonable alternative to conventional systems. The present work describes the project of an experimental setup which is focused on testing the high temperature Solid Oxide Fuel Cells (SOFC) concept as a promising innovative system. The problem of planning facilities based on fuel cell devices is faced, and the still-to-be-solved question of thermal storage is addressed. The core of the work consists of a theoretical calculation and comparison of fuel consumption for both the fuel cell and traditional systems.

Twelve case-studies on systems that generate, store and use hydrogen from photovoltaic energy are hereby presented and discussed. Hydrogen generated from direct sunlight is often called , and the whole process is characterized by having very low CO and pollutants emissions. Such systems, comprising of several sub-systems of different technologies, are called . All case-studies are briefly analyzed and the most prominent conclusions reported. Results show that production of solar hydrogen and its subsequent use in fuel cells is technically viable but costs still need to be reduced for widespread adoption. A comparison is given and need for further work highlighted; in particular, researchers should investigate carbon structures as a potential alternative to pressurization or metal hydrides; a complete analysis of the intangible costs and benefits involved should be performed, together with Discounted Cash Flow and Life Cycle Assessment analysis to understand the true nature of such investments and their sustainability in the near future. Performing such a rigorous and complete economical analysis would, for instance, enable governments to design better incentive schemes and propel such technology in real life usage.

Abstract Cotton agricultural industry is an important sector for some developing countries, whose energy consumption is dramatically rising. Here, biomass is the most important source of energy, but they are used in an inefficient way, causing atmospheric pollution and wasting resources. Combined energy generation and biochar production using cotton residues briquettes as fuel in a PP20 gasifier plant is investigated. The machine has demonstrated similar performances to its “conventional” use: 14% global efficiency and 1.16 kg/kWhel specific consumption of cotton briquettes are observed. It is calculated that one-hectare field can generate more than 4 MWh and about 130 kg of biochar per year. Biochar represents a valuable by-product; if used as amendment for cotton growth it can improve the soil conditions, both decreasing the need of fertilizers up to 50%. A circular economic model based on cotton waste gasification is proposed. Clean and affordable energy can be produced, in order to promote a sustainable development of rural areas.

Abstract Energy efficiency and thermal comfort in historic buildings are very often hampered by preservation needs. This issue is particularly relevant for historical and monumental buildings, which currently represent a large part of the historic buildings stock in Europe. For such protected buildings most of the available retrofitting solutions are not feasible and alternatives have to be investigated to guarantee their usability potential. The purpose of this study is therefore to present a methodology to evaluate the potential of electric radiant panels as retrofitting solutions for historical and monumental buildings, focusing on thermal comfort and energy saving potential when compared with conventional fossil-fuel-based heating systems. In fact, the non-invasiveness and flexibility of electrical panels make them one of the few feasible solutions for protected buildings. An original methodology is developed to evaluate the performance of such localized heating systems; the methodology is based on a dynamic simulation model, calibrated with temperature measurements, which takes into account the geometry and technical characteristics of electrical radiant panels and allows different control strategies to be compared. The methodology is applied to a relevant Italian historical building. The results show that the panels, despite their well-known low-exergy efficiency, may become a viable and attractive solution for historical buildings without undermining their preservation requirements. Apart from significantly increasing thermal comfort, electric radiant panels may also allow annual heating energy savings up to 70% for the selected building.

Downdraft stratified gasifiers seem to be the reactors which are most influenced by loading conditions. Moreover, the larger the reactor is, the higher the possibility to stumble across a channeling phenomenon. This high sensitivity is due to the limited thickness and superficial placement of the flaming pyrolysis layer coupled with the necessity to keep all the zones parallel for a correct running of this kind of gasifier. This study was aimed at modeling and investigating the channeling phenomenon generated by loading condition variations on a 250-kWe nominal power gasification power plant. The experimental campaign showed great variations in most of the plant outputs. These phenomena were modeled on two modified mathematical models obtained from literature. The results of the models confirmed the capability of this approach to predict the channeling phenomena and its dependency on the loading method.

Diesel engines are robust and reliable machine for stationary electrical energy production. In fact, these engines are designed to run continuously for thousands of hours and with low maintenance. However, several issues affect the application of syngas as fuel in this kind of engines. The full conversion from diesel to gas fuel need the presence of the spark plug instead of the diesel injection. Therefore, the high compression ratio in this kind of engines increase the possibility of the knocking phenomenon inside the combustion chamber. The knocking damages the engine mechanical structure and reduce the engine reliability. Several works set the limit of the compression ratio to 17 in order to overcome this issue. In addition, the velocity of the syngas combustion flame is higher compared to the diesel one as result to the presence of hydrogen in the syngas. This difference forces to reduce the spark ignition time from 0 to 15 ° in advance respect the Bottom Top Dead Center (BTDC) in order to limit the peak pressure inside the cylinders to the design value of the engine. Aim of this work is to compare results of a 0D mathematical model of a converted diesel engine with the results obtained in an experimental campaign. For the tests a Fiat Power Train (FPT) 4.5 liters commercial diesel engine converted to syngas is used. The model calculates the maximum power output of the engine at different rpm starting from syngas composition, air­syngas mixture temperature and diesel nominal power. The model takes into account the friction losses, air to fuel ratio and intake manifold pressure. Experimental tests were run on a gasification facility consisting in a fixed bed wood chip downdraft gasifier that generates syngas to fuel the FPT engine. The engine is connected to a MeccAlte generator for electrical power production. An Arduino based controller sets the position of the air valve in order to stabilize the lambda value of the exhaust of the engine to 1.05. A variable electrical load was applied and it was increased as long as the engine was able to drag the generator at 1500 rpm. During the tests, the following parameters were monitored: syngas volumetric flow rate and composition, syngas pollutants concentration (tar, particulate and water), air-gas mixture temperature and intake manifold pressure. An HT electrical circuit analyzer recorded the power output of the generator. Several tests were run at 1500 rpm varying the air-syngas mixture temperature and the intake manifold pressure and experimental results was compared to 0D model predictions. A good agreement of the model to experimental data was achieved. Syngas conversion reduces the maximum electrical power output of the engine generator from 49.7 kW to about 22 kW as result of the lower air-syngas mixture calorific value and density compared to diesel-air mixture. However, the engine mechanical efficiency is comparable using syngas or diesel fuel (about 30%) and pollutant emissions are strongly lower with syngas fuel. Proceedings of the 24th European Biomass Conference and Exhibition, 6-9 June 2016, Amsterdam, The Netherlands, pp. 880-883