Davide Di Battista

Development of an organic Rankine cycle system for exhaust energy recovery in internal combustion engines

Road transportation is currently one of the most influencing sectors for global energy consumptions and CO2 emissions. Nevertheless, more than one third of the fuel energy supplied to internal combustion engines is still rejected to the environment as thermal waste at the exhaust. Therefore, a greater fuel economy might be achieved recovering the energy from exhaust gases and converting it into useful power on board. In the current research activity, an ORC-based energy recovery system was developed and coupled with a diesel engine. The innovative feature of the recovery power unit relies upon the usage of sliding vane rotary machines as pump and expander. After a preliminary exhaust gas mapping, which allowed to assess the magnitude of the thermal power to be recovered, a thermodynamic analysis was carried out to design the ORC system and the sliding vane machines using R236fa as working fluid. An experimental campaign was eventually performed at different operating regimes according to the ESC procedure and investigated the recovery potential of the power unit at design and off-design conditions. Mechanical power recovered ranged from 0.7 kW up to 1.9 kW, with an overall cycle efficiency from 3.8% up to 4.8% respectively. These results candidate sliding vane machines as efficient and reliable devices for waste heat recovery applications.

Energy Recovery From the Turbocharging System of Internal Combustion Engines

On the road transportation sector, considering its deep involvement with many social expectations, assumed such proportions to become one of the major source of air pollution, mainly in urban highly congested areas.The use of reciprocating internal combustion engines (ICE) dominates the sector and the environmental dimension of the problem is under a strong attention of Governments. European Community, for instance, through sequences of regulations (EURO) reduced the emission allowed of primary pollutants; more recently, the Community added limits to climate-altering gases which directly refer to fuel consumption reduction. These limits today appear the new driver of the future engine and vehicle technological evolution. Similar efforts are under commitment by other developed countries (USA, Japan, etc,…) as well as also by the other Countries whose economic importance will dominate the markets in a very near future (BRICS Countries).The need to fulfill these issues and to keep the traditional engine expectations (torque, speed, fun to drive, etc..) triggered, especially in recent decades, a virtuous cycle whose result will be a new engine and vehicle era. The evolution till had today has been driven by the EURO limits and it demonstrated surprisingly that emission reduction and engine performances can be matched without compromises in both sides. Today, adding severe limits on equivalent CO2, emissions, it appears very difficult to predict how future engines (and vehicles) will be improved; new technologies are entering to further improve the traditional thermal powertrain but the way to a massive and more convinced electrification seems to be definitely opened.The two aspects will match in the sector of energy recovery which appears one of the most powerful tools for fuel consumption saving and CO2 reduction.When the recovery is done on exhaust gases it has an additional interest, having a moderate cost per unit of CO2 saved. The potentiality of this recovery is huge: 30%–35% of the chemical energy provided by the fuel is lost with the flue gases. For different reasons engines for passengers cars or goods transportation (light and heavy unit engines) as well those used for electricity generation (gen-set) are interested to this recovery: the first sector for the CO2 reduction, the second for the increasing value of electrical energy on the market. This wide interest is increasing the probability to have in a near future a reliable technology, being different actors pushing in this direction.In recent years the literature focused the attention to this recovery through a working fluid (organic type) on which the thermal energy is recovered by increasing its enthalpy. Thanks to a sequence of thermodynamic transformations (Rankine or Hirn cycle), mechanical work is produced. Both concept (Organic working fluid used and Rankine Cycle) are addressed as ORC technology. This overall technology has an evident complexity and doesn’t match with the need to keep reduced costs: it needs an energy recovery system at the gas side, an expander, a condenser and a pump. The space required by these components represents a limiting aspect. The variation of the flow rate and temperature of the gas (typical in ICE), as well as that at the condenser, represents additional critical aspect and call for suitable control strategies not yet exploited.In this paper the Authors studied an energy recovery method integrated with the turbocharging system, which does not require a working fluid making the recovery directly on the gas leaving the cylinders. Considering that the enthalpy drop across the turbine is usually higher than that requested by the compressor to boost the intake air, the concept was to consider an additional turbine which operates in parallel to the existing one. Room for recovery is guaranteed if one considers that a correct matching between turbine and compressor is actually done bypassing part of the exhaust gas from the turbine (waste gate) or using a variable geometry turbine (VGT) which, in any case, represents an energy loss. An additional positive feature is that this recovery does not impact on engine performances and the main components which realizes the recovery (valves & turbine) are technologically proven.In order to evaluate the potentiality of such recovery, the Authors developed a theoretical activity which represents the matching between turbocharger and engine. Thanks to an experimental characterization done on an IVECO F1C 16v JTD engine, an overall virtual platform was set up. The result produced a very satisfactory representation of the cited engine in terms of mechanical engine performances, relevant engine flow rates, pressures and temperatures. The ECU functions were represented too, such as boost pressure, EGR rates, rack control of VGT, etc…Two new direct recovery configurations have been conceived and implemented in the engine virtual platform.© 2012 ASME

Head and Block Split Cooling in ICE

The driver of the future engine technology will be the reduction of the CO2 emissions which looks straightforward to fuel consumption saving. The fulfillment of primary pollutants emission levels requested by EURO 6, LEV III or Japanese standards would still add a new innovation stimulus, but the main concept is a more efficient vehicle. Among the more interesting technologies, those related to a revision of the engine cooling, as well as, more generally, those oriented to fulfill the overall vehicle thermal needs appear very promising in terms of expected fuel saving performances. They have an additional advantage related to the low vehicles cost increase per unit of CO2 saved (or fuel saved). Thermal management is the common way to present such a technological interest and it resumes many innovations based on the idea that a vehicle is a system and all the thermal needs (of the engine and of the vehicle) should be optimized looking at the overall system and not at specific aspects. One of the main goal of thermal management is to decrease engine warm up time considering the weight of the cold phase inside the most common approval cycles. Benefits on primary pollutants emission reduction are matched with those on fuel saving, with a double positive contribution. Many technologies are already available to reach this aim, but thermal management invites to consider a number of other innovations which have to be exploited. The paper makes use of an engine mathematical model previously developed by the Authors to discuss the performances of a traditional cooling flow passage inside an existing engine and two novel circuits which try to implement a split cooling between engine head and block. If head mean temperature is kept colder and engine block warmer, engine performances can be increased reducing friction losses, warm up time and having the possibility to increase volumetric compression ratio.

Experimental and numerical analyses on a plate heat exchanger with phase change for waste heat recovery at off-design conditions

This paper analyzes the performances of an evaporator for small scale waste heat recovery applications based on bottoming Organic Rankine Cycles with net output power in the range 2-5 kW. The heat recovery steam generator is a plate heat exchanger with oil as hot stream and an organic fluid on the cold side. An experimental characterization of the heat exchanger was carried out at different operating points measuring temperatures, pressures and flow rates on both sides. The measurement data further allowed to validate a numerical model of the evaporator whereas heat transfer coefficients were evaluated comparing several literature correlations, especially for the phase-change of the organic fluid. With reference to a waste heat recovery application in industrial compressed air systems, multiple off-design conditions were simulated considering the effects of oil mass flow rate and temperature on the superheating of the organic fluid, a key parameter to ensure a proper operation of the expansion machine, thus of the energy recovery process.

The performance of a mobile air conditioning system with a water cooled condenser

Vehicle technological evolution lived, in recent years, a strong acceleration due to the increased awareness of environmental issues related to pollutants and climate altering emissions. This resulted in a series of international regulations on automotive sector which put technical challenges that must consider the engine and the vehicle as a global system, in order to improve the overall efficiency of the system. The air conditioning system of the cabin, for instance, is the one of the most important auxiliaries in a vehicle and requires significant powers. Its performances can be significantly improved if it is integrated within the engine cooling circuit, eventually modified with more temperature levels.In this paper, the Authors present a mathematical model of the A/C system, starting from its single components: compressors, condenser, flush valve and evaporator and a comparison between different refrigerant fluid. In particular, it is introduced the opportunity to have an A/C condenser cooled by a water circuit instead of the external air linked to the vehicle speed, as in the actual traditional configuration. The A/C condenser, in fact, could be housed on a low temperature water circuit, reducing the condensing temperature of the refrigeration cycle with a considerable efficiency increase.