Chemical Kinetics Study on Small-Alkane Ignition Process to Design Optimum Methane-Based Blend for HCCI

Kazunari Kuwahara; Takuya Tada; Hiroki Tanaka; Takahiro Sako; Masahiro Furutani; Yasuyuki Sakai; Hiromitsu Ando

doi:10.4271/2014-01-1281

The ignition delay times and heat release profiles of CH₄, C₂H₆, C₃H₈, i-C₄H₁₀, and n-C₄H₁₀ and dual-component CH₄-based blends with these alkanes in air were determined using a detailed chemical kinetic model. The apparent activation energy of C₂H₆ in the relationship between initial temperature and ignition delay time is higher than those of the other alkanes because OH formation is dominated by H₂O₂(+M)=OH+OH(+M) from the beginning over a wide range of initial temperatures. The heat release rate of C₂H₆ is higher than those of the other alkanes in the late stage of ignition delay time because H₂O₂ is accumulated with a higher concentration and promotes the OH formation rate of H₂O₂(+M)=OH+OH(+M). These ignition characteristics are reflected in those of CH₄/C₂H₆.

In an HCCI engine, misfire and partial combustion occur easily because the heat release rate during the ignition process after low-temperature OH chain branching and also during the ignition process bypassing low-temperature OH chain branching, becomes lower than the rate of decrease in internal energy during the expansion stroke. Partial combustion causes cycle-to-cycle variation in combustion as well as high HC emissions. Therefore, the heat release profile, which is slow in the early stage of ignition process, but more rapid than those of other fuels in the late stage, can reduce cycle-to-cycle variation in combustion. This type of profile is similar to that of CH₄/C₂H₆ for an HCCI engine targeting CH₄-based fuels.

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Chemical Kinetics Study on Small-Alkane Ignition Process to Design Optimum Methane-Based Blend for HCCI 2014-01-1281

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