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Y.Ando et aL lZmergy 30(2005)2206-2218 2213 —Qat t9A�.014431 , 0.8 ----oss2 91t. —mt�al pe af.S 0.6 ,y Phar a in 0.4 w E g Ph ase 11 0.0 x •0.2 Plies e 1 -60 .30 0 30 60 90 C"nk Angle(dq.ATDCI Fig. 10.Comparison of ennwtedve bew release se6edules for dithrem fuels at 100%WOT,1.0 air exoeas repo,hfflT timing, engine speed-2000 ming.'s—compmssion ratio,"AIDC(Atter Top Dead Center)••crank angle, As shown in Fig. 6, even in the stable range, combustion efficiency is less than 93%. This can be ascribed to the following reason.Quenching distances from a wall for hydrogen and methane arc shown in Pig.9[2].It is obvious that methane doesn't burn near a wall.Furthermore it is believed that existence of diluents makes quenching distance of methane longer than hydrogen. In general,the addition of hydrogen to gaseous filet showed little improvements of combustion on the fuel-rich side,but great improvements on fuel-lean side[3]. 3.2.2. Neat release Normalized cumulative heat release profiles of the stoichiometric mixtures of each fuel gas at WOT, minimum advance for best torque(MBT),2000 min-1 are shown in Fig. 10 Values are normalized with respect to the input energy,so that values less than one at the end of combustion correspond to unburned components and heat loss to wall. Ignition timings for each fuel gas are also noted in Fig. 10. Combustion can be divided into three phases: Phase I(the flame development phase=ignition delay), Phase II(the flame propagation phase),and Phase III(the!lame extinguishment phase)[4].Dashed lines identify each phase. Gradient of Phase II denotes combustion speed,therefore steeper gradient means higher combustion speed.By comparing gradients for each gas,it can be seen that the quickest combustion was combustion of Gas 2. This fact is contradictory to what we expect from CP. This reason may be attributed to differences in the compression ratio.Generally,increase of compresdOn ratio makes combustion speed faster,owing to increases in temperature and turbulence,and resulting in reduction of residual gas.In the case of Gas 2,compkasion ratio was greatest as 11.9,and the results of Fig. 10 indicate that increasing t compression ratios can improve the combustion of Phase II. In Phase III,compared with the sudden termination in the burning of Gas 2,combustion of Das 1 was longer and burned well.It is believed that this is due to the affect of wide flammable range of hydrogen. In LPhase I, long ignition delay of Gas 2 is very remarkable.Fig. 11 compares the cases at the same [ ignition advance.Ignition delay for Gas 2 is obviously long.This is caused by the following reasons.The transfer of spark energy to the fuel components is decreased by the presence of diluents,and combustible