( ( In ( the ( reaction chamber ) ) ) ( ( the ( exhaust gas ) ) ( ( reacts ( with ( the ( available oxygen ) ) ) ) . ) ) )
(ROOT (S (PP (IN In) (NP (DT the) (NN reaction) (NN chamber))) (NP (DT the) (JJ exhaust) (NN gas)) (VP (VBZ reacts) (PP (IN with) (NP (DT the) (JJ available) (NN oxygen)))) (. .)))
In the reaction chamber the exhaust gas reacts with the available oxygen.
(ROOT (S (NP (NNP Combustion) (NN reaction)) (VP (VBZ occurs) (SBAR (WHADVP (WRB when)) (S (NP (DT a) (NN substance)) (VP (VBZ reacts) (ADVP (RB quickly)) (PP (IN with) (NP (NN oxygen))))))) (. .)))