Improving the efficiency of turbocharged spark ignition engines for passenger cars through waste heat recovery

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 by throttling. This engine has however a much better power density, and therefore may operate at much higher BMEP values over driving cycles reducing the fuel economy penalty of the vehicle. This engine also has the advantage of the very well developed three way catalytic converter after treatment to meet future emission regulations. In these engines the efficiency may be improved recovering the waste heat, but this recovery may have ultimately impacts on both the in cylinder fuel conversion efficiency and the efficiency of the after treatment. Results of engine performance simulations are performed for an in-line four cylinder, turbocharged 1.6 liter passenger car engine with heat exchangers to recover the exhaust and the coolant waste heat and compared with the results for the engine without waste heat recovery.