Search Results

With the aim of decarbonizing the vehicles fleet, the use of hydrogen is promising solution. Hydrogen is an energy carrier, carbon-free, with high calorific value and with no CO2 and HC emissions burning in ICE. Hydrogen use in spark ignition engines has already been extensively investigated and optimized. On the other hand, its use in compression ignition engines has been little developed and, therefore, there is a lack of information regarding the combustion in ultra-lean conditions, typical of diesel engines. Several applications employ dual fuel combustion for the easy management of the PFI injection system to be applied in addition to the DI Common Rail system. However, this mode suffers from several problems regarding the management of the maximum flow rate of hydrogen into the intake. In particular, to avoid throwing hydrogen into the exhaust, injection must be started after the valve crossing.

The upcoming regulations to achieve zero-emission passenger transport present challenges for designing new ferry powertrains. The proposed work investigates the feasibility of using a Proton Exchange Membrane Fuel Cell (PEMFC) power system to power a long-haul ferry. The paper describes the zero-order cell model as well as the method for estimating cell degradation. The stack modeling, heat balance equations, and auxiliary modeling are also presented. The proposed model enables the simulation of the fuel cell under different operating conditions and includes the use of air or oxygen as an oxidizer. A thermal management strategy for the overall PEMFC system is also proposed. The model was calibrated on the characteristic curves of the PEMFC Ballard FCvelocity™ HD6 (150 kW) and validated by reproducing experimental results. Then, a real load profile of a ferry, as well as the proposed powertrain is considered as case study.

In the context of reducing carbon-dioxide (CO2) emissions, the increasing exploitation of renewable sources is expected to improve the availability of green hydrogen, which can be considered a valid alternative to gasoline and diesel fuels in the mobility sector (particularly for long-haul and heavy-duty missions). The air-hydrogen mixing plays a significant role, particularly in direct-injection spark-ignition engines. As a matter of fact, the onset of zones featuring an equivalence ratio greater than 0.5 should be avoided, since this would lead to an increased risk of self-ignition and NOx production. The presence of wide ultra-lean volumes (over the lean flammability limit) due to imperfect mixing is negative too, yielding to irregular combustion. Therefore, the calibration of the direct injection timing is a crucial task.

In this work, an ozone/air/gasoline mixture has been used as an alternative strategy to achieve a stable combustion in a spark ignition (SI) single cylinder PFI research engine. The air intake manifold has been modified to include four cells to produce ozone with different concentrations. In the research engine, various operating parameters have been monitored such as the in-cylinder pressure, temperature and composition of the exhaust gases, pressure and temperature of the mixture in the intake manifold, engine power and torque and specific fuel consumption. Experimental tests have been carried out under stoichiometric mixture conditions to observe the influence of ozone addition on the combustion process. The results show an advance and an increase of the in-cylinder pressure compared to the reference test-case, where a gasoline/air mixture is used. It is worth noting that, especially under stoichiometric condition, ozone concentration induces auto-ignition and knock.

Nowadays, the vehicle hybridization and the use of non-conventional fuels for heavy-duty applications brings to a new beginning in the use of spark ignition (SI) engines. For a standard intake system, the premixed fuel/air mixture is controlled by the injection of fuel after the throttle valve. Then, the geometry of the intake system, with the intake duct, the intake valves and the cylinder head shape, influences the characteristics of the flow within the cylinder up to the combustion process. The new technology of fluid-power and electrical actuations gives the opportunity to decouple the intake and exhaust valve actuations with respect to the standard cam shaft distribution. The Variable Valve Actuation (VVA) concept is not new, but its application is now affordable and flexible enough to be applied to partial load conditions.

1 Nowadays, In-Cylinder Pressure Sensors (ICPS) have become a mainstream technology that promises to change the way the engine control is performed. Among all the possible applications, the prediction of raw (engine-out) NOX emissions would allow to eliminate the NOX sensor currently used to manage the after-treatment systems. In the current study, a semi-physical model already existing in literature for the prediction of engine-out nitric oxide emissions based on in-cylinder pressure measurement has been improved; in particular, the main focus has been to improve nitric oxide prediction accuracy when injection timing is varied. The main modification introduced in the model lies in taking into account the turbulence induced by fuel spray and enhanced by in-cylinder bulk motion.

The incoming RDE regulation and the on-board diagnostics -OBD- pushes the research activity towards the set-up of a more and more efficient after treatment system. Nowadays, the most common after treatment system for NOx reduction is the selective catalytic reduction -SCR- . This system requires as an input the value of engine out NOx emission -raw- in order to control the Urea dosing strategy. In this work, an already existing grey box NOx raw emission model based on in-cylinder pressure signal (ICPS) is validated on two standard cycles: MNEDC and WLTC using an EU6 engine at the test bench. The overall results show a maximum relative error of the integrated cumulative value of 12.8% and 17.4% for MNEDC and WLTC respectively. In particular, the instantaneous value of relative error is included in the range of ± 10% in the steady state conditions while during transient conditions is less than 20% mainly.