Energy Recovery in Passenger Cars

Abstract

The turbocharged direct injection stoichiometric spark ignition gasoline engine has less than diesel full load brake engine thermal efficiencies and much larger than diesel penalties in brake engine thermal efficiencies reducing the load. This engine has, however, a much better power density, and therefore may operate at much higher brake mean effective pressure (BMEP) values over driving cycles thus reducing the fuel economy penalty of the vehicle. This engine also has the advantage of the very well developed three way catalytic (TWC) converter after treatment to meet future emission regulations. Replacement of fossil gasoline with renewable gasoline-like fuels has major advantages. Ethanol and methanol have larger than gasoline resistance to knock and heat of vaporization, and this ultimately translates in larger than gasoline compression ratio and boost pressure and spark advances closer to maximum brake torque producing better efficiencies both full and part load. For the specific of these novel turbocharged direct injection stoichiometric spark ignition renewable gasoline-like engines coupled to a hybrid-electric power train, the paper considers the option to boost the total fuel conversion efficiency generating both mechanical and electric energy. When the internal combustion engine operates, significant fuel energy is lost in both the exhaust and the coolant. Part of this energy is recovered here by using organic Rankine cycle (ORC) systems fitted to both the exhaust and the coolant, with their expanders driving generators charging the battery of the car. The exhaust and the coolant organic Rankine cycle are effective in increasing the amount of fuel energy converted in usable power over the full range of loads and speeds. The organic Rankine cycle system fitted on the exhaust permits to increase the usable power versus the fuel energy flow rate of a 3.4% on average, with top improvements up to 6.4%. The system is effective particularly at high speeds and loads. The organic Rankine cycle system fitted on the coolant permits to increase the usable power versus the fuel energy flow rate of a 1.7% on average, with top improvements up to 2.8%. The system is effective particularly at low speeds and loads. The two combined organic Rankine cycle systems permit to increase the usable power versus the fuel energy flow rate of a 5.1% on average, with top improvements up to 8.2%.