There is significant interest in using hydrogen and natural gas for enhancing the performance of diesel engines. We report herein a numerical investigation on the ignition of n-C 7 H 16 /H 2 and n-C 7 H 16 /CH 4 fuel blends. The CHEMKIN 4.1 software is used to model ignition in a closed homogenous reactor under conditions relevant to diesel/HCCI engines. Three reaction mechanisms used are (i) NIST mechanism involving 203 species and 1463 reactions, (ii) Dryer mechanism with 116 species and 754 reactions, and (iii) a reduced mechanism (Chalmers) with 42 species and 168 reactions. The parameters include pressures of 30atm and 55atm, equivalence ratios of =0.5, 1.0 and 2.0, temperature range of 800-1400K, and mole fractions of H 2 or CH 4 in the blend between 0-100%. For n-C 7 H 16 /air mixtures, the Chalmers mechanism not only provides closer agreement with measurements compared to the other two mechanisms, but also reproduces the negative temperature coefficient regime. Consequently, this mechanism is used to characterize the effects of H 2 or CH 4 on the ignition of n-C 7 H 16 .Results indicate that H 2 or CH 4 addition has a relatively small effect on the ignition of n-C 7 H 16 /air mixtures, while the n-C 7 H 16 addition even in small amount modifies the ignition of H 2 /air and CH 4 /air mixtures significantly. The n-C 7 H 16 addition decreases and increases the ignition delays of H 2 /air mixtures at low and high temperatures, respectively, while its addition to CH 4 /air mixtures decreases ignition delays at all temperatures. The sensitivity analysis indicates that ignition characteristics of these fuel blends are dominated by the pyrolysis/oxidation chemistry of n-heptane, with heptyl (C 7 H 16 -2) and hydoxyl (OH) radicals being the two most important species.

Cryogenic fluids are used for wide range of industrial and laboratory applications. Vacuum or super-insulated transfer lines are efficiently used to transfer these fluids from the storage Dewars to the end applications. As the heat transfer to the cryogens flowing through the transfer line cannot be completely eliminated, many a times two-phase flow occurs during the transfer process. It is necessary to estimate the quality of the flow (void fraction) and the amount of cryogen being evaporated in the transfer process. Many techniques are available to measure the void fraction, but implementing these techniques to cryogenic fluid flow is sometimes difficult and expensive. Capacitance measurement is easy and simple method to find the liquid level and void fraction. Towards this, an attempt has been made to design void fraction measurement sensor based on capacitance measurement. Most of the capacitance sensors are made with inner glass tube, which needs special attention in handling the device and also it is difficult to make the end connections for the glass tubes. The present work deals with the design optimization of Hylam™ (Bakelite) and fibre-reinforced plastic (FRP) inner tube concave plate capacitance sensors for liquid nitrogen level measurement. 3-D modelling and thermo structural analysis of the developed sensors has been carried out in ANSYS workbench and electrostatic analysis has been carried out using ANSYS Maxwell software. The results obtained by the analysis have been validated with experimental results.