▁efficiency ▁for ▁example ▁of ▁B 1 0 0 ▁as ▁compared ▁to ▁B 2 0 ▁will ▁vary ▁due ▁to ▁the ▁differ ing ▁energy ▁content ▁of ▁the ▁various ▁bl ends . ▁Th erm al ▁efficiency ▁of ▁a ▁fuel ▁is ▁based ▁in ▁part ▁on ▁fuel ▁characteristics ▁such ▁as : ▁vis cos ity , ▁specific ▁density , ▁and ▁flash ▁point ; ▁these ▁characteristics ▁will ▁change ▁as ▁the ▁bl ends ▁as ▁well ▁as ▁the ▁quality ▁of ▁b iod ies el ▁var ies . ▁The ▁American ▁Society ▁for ▁Test ing ▁and ▁Material s ▁has ▁set ▁standards ▁in ▁order ▁to ▁judge ▁the ▁quality ▁of ▁a ▁given ▁fuel ▁sample . ▁ ▁One ▁study ▁found ▁that ▁the ▁bra ke ▁thermal ▁efficiency ▁of ▁B 4 0 ▁was ▁superior ▁to ▁traditional ▁pet role um ▁counter part ▁at ▁higher ▁compression ▁r ati os ▁( this ▁higher ▁bra ke ▁thermal ▁efficiency ▁was ▁recorded ▁at ▁compression ▁r ati os ▁of ▁ 2 1 : 1 ). ▁It ▁was ▁noted ▁that , ▁as ▁the ▁compression ▁r ati os ▁increased , ▁the ▁efficiency ▁of ▁all ▁fuel ▁types ▁– ▁as ▁well ▁as ▁bl ends ▁being ▁tested ▁– ▁increased ; ▁though ▁it ▁was ▁found ▁that ▁a ▁bl end ▁of ▁B 4 0 ▁was ▁the ▁most ▁econom ical ▁at ▁a ▁compression ▁ratio ▁of ▁ 2 1 : 1 ▁over ▁all ▁other ▁bl ends . ▁The ▁study ▁imp lied ▁that ▁this ▁increase ▁in ▁efficiency ▁was ▁due ▁to ▁fuel ▁density , ▁vis cos ity , ▁and ▁he ating ▁values ▁of ▁the ▁fu els . ▁ ▁Com b ust ion ▁F uel ▁systems ▁on ▁some