Low-Emission, Fuel-Flexible Combustion of Liquid Fuels - Novel Combustion Concepts for Sustainable Energy Development - page 454

Ganan-Calvo ( 2005 ), our research group has developed the FB atomization concept
to achieve low-emission combustion for a range of liquid fuels. Next, we present
important

findings and results from several application examples by our research

group.

4 Low-Emission Diesel Combustion

As first step, the combustion performance of a commercially available AB injector

and an in-house-built FB injector is compared for ow rates,

while the split between the atomizing air and combustion air is varied. The injector
performance is characterized by measuring the emissions of NO X and CO. Details
of the experimental setup are described by Panchasara et al. ( 2009a ). Brie

fixed fuel and total air fl

y, the
combustion air enters the combustor through a swirler with swirl number of 1.5.
The bulk axial inlet velocity of the primary air is 1.9

fl

2.1 m/s, which resulted in the
inlet Reynolds number varying from 5,960 to 6,750. The combustor is 8.0 cm ID
and 46-cm-long quartz tube, and it is cooled by natural convection on the back side.
A commercial AB atomizer (Delavan Siphon type 30609-2 SNA-0.20 nozzle) is
used for baseline experiments. This commercial version creates a swirling

-

flow of
atomizing air to breakdown the fuel jet as it exits the orifice plate. The air swirler
within the injector is replaced with a spacer tube to implement the FB concept
presented in Fig. 2 . In this latter con

fl

guration, air and fuel mix together before

exiting through the ori ce plate to form the spray downstream. One notable dif-

ference between the two injectors is the exit diameter of the injector; 0.4 mm for the
AB injector versus 1.5 mm for the FB injector. Figure 3 illustrates the two injector
designs and highlights the

fl flow paths for fuel and atomizing air.

flow rates of fuel and total air (combustion + atomizing) are constant,
respectively, at 12 ml/min and 150 standard liters per minute (slpm). Combustion
performance is strongly dependent upon the spray quality determined by the
atomizing air

The fl

ow rate. Thus, experiments were conducted by varying the per-
centage of the atomizing air (AA)

fl

fl flow rate in the range of 10 25 % of the total

-

air ow rate, depending upon the fuel and injector type. Since the total air-to-fuel

mass ratio is constant for all experiments, effects of atomizing air

fl

fl ow rate, injector

(a) (b)

Fuel Fuel

Air Air

Fig. 3 Detailed view of fl fluid paths in: a air-blast and b fl flow-blurring injectors