▁at ▁over ▁. ▁ ▁The ▁reason ▁for ▁high ▁pressure ▁Maxim ising ▁the ▁efficiency ▁of ▁a ▁heat ▁engine ▁depends ▁fund ament ally ▁upon ▁getting ▁the ▁temperature ▁at ▁which ▁heat ▁is ▁accepted ▁( i . e . ▁raising ▁steam ▁in ▁the ▁bo iler ) ▁as ▁far ▁as ▁possible ▁from ▁the ▁temperature ▁at ▁which ▁it ▁is ▁rejected ▁( i . e . ▁the ▁steam ▁when ▁it ▁leaves ▁the ▁cyl inder ). ▁This ▁was ▁quant ified ▁by ▁Nicolas ▁Lé on ard ▁S adi ▁Car not . ▁ ▁There ▁are ▁two ▁options : ▁raise ▁the ▁accept ance ▁temperature ▁or ▁lower ▁the ▁re jection ▁temperature . ▁For ▁a ▁steam ▁engine , ▁the ▁former ▁means ▁raising ▁steam ▁at ▁higher ▁pressure ▁and ▁temperature , ▁which ▁is ▁in ▁engineering ▁terms ▁fairly ▁straightforward . ▁The ▁latter ▁means ▁bigger ▁cyl ind ers ▁to ▁allow ▁the ▁exhaust ▁steam ▁to ▁expand ▁further ▁- ▁and ▁going ▁this ▁direction ▁is ▁limited ▁by ▁the ▁loading ▁gauge ▁- ▁and ▁possibly ▁cond ens ing ▁the ▁exhaust ▁to ▁further ▁lower ▁the ▁re jection ▁temperature . ▁This ▁tends ▁to ▁be ▁self - de fe ating ▁because ▁of ▁fr ict ional ▁losses ▁in ▁the ▁greatly ▁increased ▁volumes ▁of ▁exhaust ▁steam ▁to ▁be ▁handled . ▁ ▁Thus ▁it ▁has ▁often ▁been ▁considered ▁that ▁high ▁pressure ▁is ▁the ▁way ▁to ▁go ▁to ▁improve ▁locomot ive ▁fuel ▁efficiency . ▁However , ▁experiments ▁in ▁this ▁direction ▁were ▁always ▁defeated ▁by ▁much ▁increased ▁purchase ▁and ▁maintenance ▁costs . ▁A ▁simpler ▁way ▁to ▁increase ▁the ▁accept ance ▁temperature ▁is ▁to ▁use ▁a ▁mod est ▁steam ▁pressure ▁and ▁a ▁super he