Browse Publications Technical Papers 2020-01-0343
2020-04-14

Experimental and kinetic investigation of pressure and temperature effects on burning characteristics of n-heptane/air/hydrogen up to near lean burn limits 2020-01-0343

Incomplete-combustion and misfire are the hurdles in diesel engines to run on ultra-lean mixture, whereas high thermal efficiency has been achieved at lean mixture. The burning characteristics of n-heptane with 0% and 30% hydrogen was studied at λ=0.8-2.0, 393K-453K and 100kPa-300kPa up to near lean explosion limits. The flame appeared spherically at 37-mJ ignition energy (IE) and excess air coefficient between 0.8 and 1.5, but further lean mixture, ≥1.6, ignited at 3000-mJ. The higher IE was the cause of unstable and distorted flame, and wrinkles at λ=1.6-1.8. The buoyancy appeared at λ ≥1.8, 393K and 100kPa. The highest burning velocity of 19.83 cm/s was observed by Chemkin at λ=1.8 under buoyancy effect. The thermal instability under impact of initial pressure and temperature was higher at lean mixture than stoichiometric mixture. The ultra-lean mixtures from λ=1.8 to λ=1.6 at 393K, λ=1.9 to λ=1.7 at 423K and λ=2.0 to λ=1.8 at 453K were under the impact of buoyancy when initial pressure was increased from 100kPa to 300kPa (higher initial pressure, more λ under buoyancy effect). The change in initial temperature, from 393K to 423K, decreased the buoyancy region from λ=1.8 to λ=2.0 at 100kPa, λ=1.7 to λ=1.9 at 200kPa and λ=1.6 to λ=1.8 at 300kPa. On behalf of a good agreement between experimental and simulation data, it was concluded that the mixture could be ignited at 37-mJ, 393K and 100kPa if the mixtures had the quantity of OH mole fraction between 8.444710-3 and 5.202810-3 for H2=0% and between 8.627410-3 and 5.249410-3 for H2=30%. However, the mole fraction quantity less than 5.202810-3 for H2=0% and 5.249410-3 for H2=30% could be ignited at 3000-mJ. The quantity of mole fraction <3.015910-3 for H2=0% and <3.055610-3 for H2=30% was insufficient to prevent radiation from losses due to low burning velocity, and flame would buoy.

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