Internal Combustion Engine Group OH and NO distributions in combusting diesel sprays 13 June 2006 Romain Demory

Outline Introduction Diesel combustion and nitrogen oxides Laser-Induced Fluorescence Validity and limitations Results and Discussion Flame development and nitric oxide formation Conclusions

Introduction Aim: Identify the conditions leading to the formation of NO in combusting diesel sprays (1) Characterise the combustion in time and space (2) Acquire spatially and temporally precise distributions of NO Instrumented engineVideos of the spray/flame Combustion marker: OH-LIF : NO-LIF 2/15

Laser-Induced Fluorescence Correction Model 3/15 1) Population (Boltzmann) distribution 2) Broadening and shift 3) Collisional Quenching temperature dependent overlap integral is rather constant over the range of pressure and temperature can be evaluated if local temperature and molar fractions of colliding species are know

Laser-Induced Fluorescence Correction Model 4) Model 180° 1) Pre-mixed volume 2) Mixing-controlled volume Integration of the heat release rate in time gives a local temperature Combustion is scaled on heat release rate to obtain local χ CO 2 χ H 2 O χ O 2 8/15

Laser-Induced Fluorescence Correction Model 5) Model results Temperature evolution Stern-Vollmer (yield) factorBoltzmann (population) factor 1.9 ms2.3 ms2.8 ms3.3 ms4.0 ms 9/15

Results and discussion Raw OH-LIF results Laser attenuation is visible (brighter on left side) All images are for the same timing, different cycles Injection of 30 mm³ of fuel in a quiescent air at 630 K and 5 MPa Injection pressure: 100 MPa OH is found in the flame front The flame front is heavily rippled and unevenly thick Even in a quiescent air environment, the spray development and evaporation leads to a rippled diffusion flame 10/15

Results and discussion OH flame NO 3 OH (simulation) time [ms aSOI] laser sheet height Injection pressure: 100 MPa Injected volume: 30 mm³ In-cylinder presssure: 5 MPa In-cylinder temperature: 630 K Summary 11/15

Results and discussion Natural flame luminosity + external lights 12/15

Results and discussion Summary 13/15

Conclusion Pre-mixed phase: Very short and mostly invisible to the optical techniques employed The heat release rate remains the best indicator of the beginning of the combustion chemistry Mixing-controlled phase: Varying but sometimes very early start of the diffusion flame Part of the “pre-mixed spike” in the heat release rate could be attributed to the diffusion flame. Whereas the flame front is rather stable downstream of the evaporation zone, the combustion near the tip of the spray is more chaotic and becomes increasingly richer, possibly leading to high concentrations of soot in the late part of the combustion. Nitric oxide formation: No fluorescence detected from the pre-mixed combustion (too rich or/and too short) as reported by Dec (1998) NO distributions moved downstream as the diffusion flame developed, no structured pattern was detected during the stabilised diffusion flame (can be partially explained by the Stern-Vollmer factor and the Boltzmann distribution) 14/15

Thank you 15/15 Questions?