  We use the 2011 Rossi X-ray Timing Explorer (RXTE) proportional counter array
(PCA) data of the 401 Hz accreting pulsar and burster IGR J17498-2921 to
perform timing analysis and time-resolved spectroscopy of 12 thermonuclear
X-ray bursts. We confirm previously reported burst oscillations from this
source with a much higher significance (8.8\sigma). We notice that the bursts
can be divided into three groups: big photospheric radius expansion (PRE)
bursts are about ten times more luminous than medium bursts, while the latter
are about ten times more luminous than small bursts. The PCA field-of-view of
these observations contains several known bursters, and hence some of the
observed bursts might not be from IGR J17498-2921. The oscillations during big
bursts at the known pulsar frequency show that these bursts were definitely
from IGR J17498-2921. We find that at least several of the other bursts were
also likely originated from IGR J17498-2921. Spectral analysis reveals that the
luminosity differences among various bursts are primarily due to differences in
normalizations, and not temperatures, even when we consider the effects of
colour factor. This shows burning on a fraction of the stellar surface for
those small and medium bursts, which originated from IGR J17498-2921. The low
values of the upper limits of burst oscillation amplitude for these bursts
suggest a small angle between the spin axis and the magnetic axis. We find
indications of the PRE nature of a medium burst, which likely originated from
IGR J17498-2921. If true, then, to the best of our knowledge, this is the first
time that two PRE bursts with a peak count rate ratio of as high as {\approx}
12 have been detected from the same source.
