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This work presents the autoignition delay time characteristics of methane and natural gas under simulated diesel engine conditions. A constant-volume combustion vessel is used for the experiments. Results are presented for the pressure and temperature ranges of 5 to 55 atm and 600 to 1700 K, respectively. Comparisons are then made with autoignition data for methanol, ethanol, isooctane, and n-cetane. Three major trends are observed. First, there is little effect on the autoignition delay time of natural gas as the vessel pressure is increased from 5 to 55 atm. Second, there is a slight decrease in the autoignition delay time of methane-ethane gas mixtures as the concentration of ethane is increased. Third, the autoignition delay time of natural gas is strongly dependent on temperature and continually decreases with increasing temperature.

The effects of ambient gas thermodynamic state and fuel composition on the autoignition of natural gas under direct-injection diesel conditions were studied experimentally in a constant-volume combustion vessel and computationally using a detailed chemical kinetic model. Natural gas compositions representative of variations observed across the U.S. were considered. These results extend previous observations to more realistic natural gas compositions and a wider range of thermodynamic states that include the top-dead-center conditions in the natural gas version of the 6V-92 engine being developed by Detroit Diesel Corporation. At temperatures less than 1200 K, the experiments demonstrated that the ignition delay of natural gas under diesel conditions has a dependence on temperature that is Arrhenius in character and a dependence on pressure that is close to first order.

Methanol and ethanol are being considered as alternative fuels for diesel engines. One of the key concerns with using alcohol fuels in diesel engines is their poor ignition quality. This work presents the ignition characteristics of methanol and ethanol examined under simulated diesel engine conditions in a constant-volume combustion vessel. The ignition characteristics of isooctane and normal hexadecane (cetane) measured under the same conditions are also included for reference. Results show that to obtain ignition delays and rates-of-pressure-rise suitable for current diesel engine designs, methanol and ethanol require in-cylinder temperatures of about 1100 K at the time of injection. The results also show that the ignition delays of the alcohol fuels are independent of the chamber pressure and are unaffected by the presence of 10% by volume of water in the fuel.

The maximum extent of liquid-phase fuel penetration into in-cylinder gases is an important parameter in compression-ignition (CI) engine design. Penetration of the fuel is needed to promote fuel-air mixing, but over-penetration of the liquid phase and impingement on the bowl wall can lead to higher emissions. This maximum liquid-phase fuel penetration, or “liquid length,” is a function of fuel properties, in-cylinder conditions, and injection characteristics. The goal of this study was to measure and correlate the liquid lengths of fuels with wide physical property variations. The fuels were injected into a large range of in-cylinder temperature (700 to 1300 K) and density (3.6 to 59.0 kg/m3) conditions, at an injection pressure (140 MPa) that is characteristic of those provided by current high-pressure injection equipment.