The paper describes a numerical study of the combustion of hydrogen enriched methane and biogases containing hydrogen in a Controlled Auto Ignition engine (CAI). A single cylinder CAI engine is modelled with Chemkin to predict engine performance, comparing the fuels in terms of indicated mean effective pressure, engine efficiency, and pollutant emissions. The effects of hydrogen and carbon dioxide on the combustion process are evaluated using the GRI-Mech 3.0 detailed radical chain reactions mechanism. A parametric study, performed by varying the temperature at the start of compression and the equivalence ratio, allows evaluating the temperature requirements for all fuels; moreover, the effect of hydrogen enrichment on the auto-ignition process is investigated. The results show that, at constant initial temperature, hydrogen promotes the ignition, which then occurs earlier, as a consequence of higher chemical reactivity. At a fixed indicated mean effective pressure, hydrogen presence shifts the operating range towards lower initial gas temperature and lower equivalence ratio and reduces NOx emissions. Such reduction, somewhat counter-intuitive if compared with similar studies on spark-ignition engines, is the result of operating the engine at lower initial gas temperatures.

Overtopping-type wave power conversion devices represent one of the most promising technology to combine reliability and competitively priced electricity supplies from waves. While satisfactory hydraulic and structural performance have been achieved, the selection of the hydraulic turbines and their regulation is a complex process due to the very low head and a variable flow rate in the overtopping breakwater set-ups. Based on the experience acquired on the first Overtopping BReakwater for Energy Conversion (OBREC) prototype, operating since 2016, an activity has been carried out to select the most appropriate turbine dimension and control strategy for such applications. An example of this multivariable approach is provided and illustrated through a case study in the San Antonio Port, along the central coast of Chile. In this site the deployment of a breakwater equipped with OBREC modules is specifically investigated. Axial-flow turbines of different runner diameter are compared, proposing the optimal ramp height and turbine control strategy for maximizing system energy production. The energy production ranges from 20.5 MWh/y for the smallest runner diameter to a maximum of 34.8 MWh/y for the largest runner diameter.

Organic Rankine Cycle (ORC) power plants are characterized by high efficiency and flexibility, as a result of a high degree of maturity. These systems are particularly suited for recovering energy from low temperature heat sources, such as exhaust heat from other plants. Despite ORCs having been assumed to be appropriate for stationary power plants, since their layout, size and weight constraints are less stringent, they represent a possible solution for improving the efficiency of propulsion systems for road transportation. The present paper investigates an ORC system recovering heat from the exhaust gases of an internal combustion engine. A passenger car with a Diesel engine was tested over a Real Driving Emission (RDE) cycle. During the test exhaust gas mass flow rate and temperature have been measured, thus calculating the enthalpy stream content available as heat addition to ORC plant in actual driving conditions. Engine operating conditions during the test were discretized with a 10-point grid in the engine torque–speed plane. The ten discretized conditions were employed to evaluate the ORC power and the consequent engine efficiency increase in real driving conditions for the actual Rankine cycle. N-pentane (R601) was identified as the working fluid for ORC and R134a was employed as reference fluid for comparison purposes. The achievable power from the ORC system was calculated to be between 0.2 and 1.3 kW, with 13% system efficiency. The engine efficiency increment ranged from 2.0% to 7.5%, with an average efficiency increment of 4.6% over the RDE test.

The exhaust heat of energy conversion systems can be usefully recovered by Organic Rankine Cycles (ORC) instead of wasting it into the environment, with benefits in terms of system efficiency and environmental impact. Rankine cycle technology, consolidated in stationary power plants, has not yet spread out into transport applications due to the layout limitations and to the necessity of containing the size and weight of the ORC system. The authors investigated an ORC system bottoming a compression ignition engine for marine application. The exhaust mass flow rate and temperature, measured at different engine loads, have been used as inputs for modeling the ORC plant in a Simulink environment. An energy and exergy analysis of the ORC was performed, as well as the evaluation of the ORC power at different engine loads. Two different working fluids were considered: R1233zd(e), an innovative fluid belonging to the class of hydrofluoroolefin, still in development but interesting due to its low flammability, health hazard, and environmental impact, and R601, a hydrocarbon showing a benchmark thermodynamic performance but highly flammable, considered as a reference for comparison. Three plant configurations were investigated: single-pressure, dual-pressure, and reheating. The results demonstrated that the dual-pressure configuration achieves the highest exploitation of exhaust heat. R1233zd(e) produced an additional mechanical power of 8.0% with respect to the engine power output, while, for R601, the relative contribution of the ORC power was 8.7%.

Waste heat recovery can be a key solution for improving the efficiency of energy conversion systems. Organic Rankine Cycles (ORC) are a consolidated technology for achieving such target, ensuring good efficiencies and flexibility. ORC systems have been mainly adopted for stationary applications, where the limitations of layout, size and weight are not stringent. In road transportation propulsion systems, the integration between the powertrain and the ORC system is difficult but still possible. The authors investigated an ORC system bottoming a spark ignited internal combustion engine (ICE) powering a public transport bus. The bus, fuelled by natural gas, was tested in real driving conditions. Exhaust gas mass flow rate and temperature have been measured for calculating the thermal power to be recovered in the ORC plant. The waste heat was then used as energy input in a model simulating the performance of an ORC system. The heat transfer between the exhaust gases and the ORC fluid is crucial for the ORC performance. For this reason, attention was paid to considering the interaction between hot fluid temperature and ORC maximum pressure. ORC performance in terms of real cycle efficiency and power produced were calculated considering n-Pentane as working fluid. The fuel consumption was reduced from 271.5 g/km to 261.4 g/km over the driving cycle, corresponding to 3.7% reduction.