Catalyzes the NAD(+)-dependent dehydrogenation of 2-dehydro-3-deoxy-L-rhamnonate to form 2,4-didehydro-3-deoxy-L-rhamnonate. Does not show any detectable activity in the presence of NADP(+). 2-dehydro-3-deoxy-L-rhamnonate + NAD(+) = 2,4-didehydro-3-deoxy-L-rhamnonate + H(+) + NADH kcat is 51.8 min(1-) with 2-dehydro-3-deoxy-L-rhamnonate as substrate. kcat is 11 min(1-) with 2-dehydro-3-deoxy-L-lyxonate as substrate. kcat is 0.72 min(1-) with 2-dehydro-3-deoxy-L-mannonate as substrate. Carbohydrate degradation; L-rhamnose degradation. Homotetramer. Belongs to the short-chain dehydrogenases/reductases (SDR) family.