Thermodynamic Characteristics of Premixed Compression Ignition Combustions

Thermodynamic characteristics of premixed compression ignition combustions were clarified quantitatively by heat balance estimation. Heat balance was calculated from temperature, mole fractions of intake and exhaust gases, mass and properties of fuels. Heat balance estimation was conducted for three types of combustion; a conventional diesel combustion, a homogeneous charge compression ignition (HCCI) combustion; fuel is provided and mixed with air in an intake pipe in this case, and an extremely early injection type PREmixed lean DIesel Combustion (PREDIC). The results show that EGR should be applied for premixed compression ignition combustion to complete combustion at lower load conditions and to control ignition timing at higher load conditions. With an application of EGR, both HCCI and PREDIC showed low heat loss characteristics at lower load conditions up to 1/2 load. HCCI + EGR showed the highest indicated thermal efficiency in all load conditions over 1/2 load, which is the high load operating limit of HCCI. The indicated thermal efficiency of PREDIC + EGR showed in the middle of HCCI and conventional diesel combustion. PREDIC still requires further optimization.