Energy Recovery From the Turbocharging System of Internal Combustion Engines
Authors: Cipollone Roberto , Di Battista Davide , Gualtieri Angelo 
Published: December 2013

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.