Activities in the Laboratoire de Combustion et de Détonique (UPR9028 du CNRS)

- Detonations of CnHm/H2/N2/O2 mixtures (H.N. Presles, D. Desbordes)- Modeling of Turbulent premixed flames H2-air (M. Champion) - Non premixed swirl stabilized flames CnHm/H2/air (J.M. Most)- Auto ignition of H2-CH4 mixtures in engines (M. Bellenoue)

GDR-E Franco-ItalienKick off meeting, 10 November 2005 Orléans

Hydrogen hazards Recent results (1) :

Detonability of H2/O2/N2 mixtures as a function of :- mixture ratio : 0,21 ≤ Φ ≤ 2,4- nitrogen dilution : (H2-O2) 0 ≤ β=N2/O2 ≤ 3,76 (H2-air)- initial pressure : 0,2 bar ≤ P0 ≤ 1,5bar- initial temperature : 293K ≤ T0 ≤ 473K

Dilution of H2-O2 mixtures (Φ=1) with - O2 (towards lean mixtures )- N2 (towards H2-air mixtures)=> in each case detonability of initial mixture is maintained for large parameter variation i.e.: 0,5 ≤ Φ ≤ 1 and 0 ≤ β=N2/O2 ≤ 1

Detonability is mainly controlled by ρ0 : higher ρ0 = higher detonability

A T0 increase (293K ≤ T0 ≤ 473K) induces :- a large increase of H2-air mixtures detonability- a low decrease of H2-O2 mixture detonability

Hydrogen hazards Recent results (2) :

• Detonability of stoichiometric CH4/H2/O2/N2 mixtures:

with 0 ≤x ≤ 1 and 0 ≤ β ≤ 3,76 at P0 = 1bar and T0 = 293K ; 473K

Binary CH4-H2-air mixture:=> β = 3,76 : x = 1 (H2-air) high detonabilityx = 0 (CH4-air) low detonability

detonability controlled by the heaviest fuel: The replacement of 20% in moles of CH4 by H2

does not change the mixture detonability => Valid for other CnHm/H2 mixtures

)()5,12()1( 2242 NOxCHxHx

Hydrogen hazards Recent results (3) :

• Study of the Deflagration-to-Detonation Transition in tube of stoichiometric H2/O2/N2 mixtures:

Characterization of TDD obtained from flame acceleration in obstacles laden tubes (inner diameter d and blockage ratio BR=0.5)

When N2 dilution is increased the run up distance to obtain a detonation (LDDT) is increased

Scaling law:LTDD can be scaled with the caracteristic detonation

cell size : λ = f ( Φ, β, P0 ) LTDD ~ 36 (± 1) . λ for d/λ > 1

Hydrogen hazardsCurrent Studies :

• Safety of propulsion nuclear reactor :Reduction of the detonability of H2-air mixtures by N2 injection . (TECHNICATOME contract)

• Operational safety of fuel cells shiped on satellite : Explosion risk of H2-O2 mixtures under 70bar. (SAFT contract)

Hydrogen hazards Projects :

• Effect of concentration gradients in H2-air mixtures on :

- Inflammability- Deflagration Propagation Regimes - Deflagration-to-Detonation

Transition- Detonation Propagation Regimes

Theoretical study of turbulent O2-H2 turbulent flame adjacent to a wall• The flow of reactive mixture is a stagnating

turbulent flow , impinging on a solid wall and the intensity of turbulence is low.

• Chemistry is represented by a 3-step reduced global mechanism.

• Mean chemical rate are calculated through a 2 or 3 dimensional PDF

• Specific properties of H2 are taken into account.

Effects of H2 addition on a Non-Premixed

Swirl Stabilized CH4 Flame

Fabio CozziLaboratorio di Combustione

PoliMI-LCPolitecnico di Milano, Milano, Italy

3 month stay –April to July 2005 in Poitiers

Jean-Michel MostLaboratoire de Combustion et de Détonique

LCD , UPR 9028 du CNRSENSMA, Poitiers, France

Motivations• Why use Hydrocarbon+H2 fuels blend?

small % of H2 should improve flame stabiliy at very lean condition allowing the NOx emission reduction,

high % of H2 to reduce CO2 emission.

MHV, LHV fuels from biogass or crude oil refinery by-products contains some % of H2

• Which is the impact of fuels mixture on flame stability, pollutant emissions and soot formation?

• The combustion of Hydrocarbon+H2 is still scarcely understood.

Objectives Experimental study of the effect of H2 addition to an overall lean CH4 swirl stabilized

diffusion flame. Flame structure and flow field modifications Flame stability Pollutant emission

Compare the results obtained on different burner geometry. PoliMI 20 kW non-premixed burner (laboratory) - PIV, LDV, Rayleigh Scattering, ... LCD 40 kW non-premixed burner (industrial) - ICCD (2D spontaneous emission), PLIF, PIV,

LDV.

PoliMI-LC

Burner ConfigurationMaximum Input Thermal Power: 20kWAir: Swirled air (tang & axial inlet)Fuel: NG+H2 (0% up to 100% H2)

Fuel injection: axial/radial

36 mm

8 mm

Swirled air flow Fuel

Burner Head

Burner ConfigurationMaximum Input Thermal Power: 40kWAir: Swirled air (tang & axial inlet)Fuel: CH4+H2 (0% up to 20% H2)

Fuel injection: axial

Different quarl geometries are available

25°

CNRS-LCD

PoliMI-LCLCD

PoliMI-LC vs LCD Flame~0.7, S~1

Fuel = 100% GN (~90% CH4)20 kW

~0.7, S~0.8 Fuel = 100% CH4

40 kW

texp= 1 stexp= 0.02 s

100% GN 50% GN + 50% H2 20% GN+80% H2100% H2=0.71 =0.44 =0.28 =0.17

PIV Field of View

PoliMI-LC: Effect of H2 addition

• The blue zone of the flame (CH* emission) decreases in size

• The blue zone moves towards the burner head

• A central yellow plume is clearly observable

• At 100% H2 the flame has a reddish color likely due to H2O

Unfiltered Flame Spontaneous Emission

PoliMI-LC: Experimental ResultsEffects of H2 addition1) Flame Stability increases (burner can operate at overall leaner

condition). 2) NOx and CO emissions increase as H2 increases from 0% to

80%.3) Increase in Soot formation (qualitatively).4) Fuel jet penetration increases.

Changing fuel injection configuration 1) The yellow plume disappeared.2) CO emission increases (as compared to axial injection).3) NOx emission decreases (as compared to axial injection).

Operating Conditions: S=0.8, ~ 0.7, Thermal Power = 40 kW. (F# 4.8, texp=1/25 s)

0 % H2 20 % H2

LCD: Spontaneous Emission (1/3)

10 % H2

Hydrogen addition up to 20% by volume induces small changing in the visible flame shape!

Operating Conditions: S=0.8, ~ 0.7, Thermal Power = 40 kW. ICCD, average of 200 frames, texp=15 s

LCD: CH*, OH* Chemiluminescence

CH*

(430 nm)

OH*

(310 nm)

0 % H2 20 % H2

Operating Conditions: S=0.8, ~ 0.7, Thermal Power = 40 kW. ICCD, average of 200 frames, texp=15 s

LCD: CH*, OH* Chemiluminescence

CH*

(430 nm)

OH*

(310 nm)

0 % H2 20 % H2

Filtered spontaneous emission images highlight small changing in the flame shape.

H2 addition shorten the regions CH* of OH* emission.

The distribution of reaction zone (based on CH* and OH* emission) appears to be spatially more uniform.

0 % H2 20 % H2

LCD: Spontaneous Emission (2/3)

10 % H2

Operating Conditions: S=0.4, ~ 0.7, Thermal Power = 40 kW. (F# 2, texp=1/50 s)

Hydrogen addition up to 20% by volume induces small changing in the visible flame shape!

Operating Conditions: S=0.4, ~ 0.7, Thermal Power = 40 kW. ICCD, average of 200 frames, texp=15 s

CH*

(430 nm)

LCD: CH*, OH* Chemiluminescence

0 % H2 20 % H2

Filtered spontaneous emission images highlight small changing in the flame shape.

The distribution of the reaction zone (based on CH* emission) appears to be spatially more uniform.

LCD: Spontaneous Emission (3/3)

0 % H2 40 % H220 % H2

Operating Conditions: S>0.8, ~ 0.7, Thermal Power = 20 kW. (F# 2, texp=1/350 s)

Hydrogen addition of 40% by volume induces a significant change in the visible flame shape!

LCD: Conclusions The existing LCD burner has been set up to burn CH4+H2 fuel mixture.

Several Filtered and Unfiltered image of the spontaneous flame emission has been collected under different experimental condition.

Effects of H2 addition up to 20% by volume (40 kW) Small effect on the visible flame shape. Qualitatively: no relevant changes in burner stability (when using the quartz quarl).

At =0.7 no change in the minimum swirl number before flame blow-off (S~0.15).

THIS SWIRL STABILIZED FLAME IS VERY STABLE!

NEGLIGIBLE EFFECTS OF 20% H2 ADDITION ON A SWIRL STABILIZED DIFFUSION FLAME !??