Masahiro Taki

Rotational relaxation in free jet expansion for N2 from 300 to 1000 K

The object of this study is to obtain information on the rotation–translation transition probability during N2–N2 collisions. Rotational relaxation for N2 in the free expansion flow is studied by TOF (time‐of‐flight) measurement with a molecular beam sampling mass filter system. Source temperatures were heated up to 1300 K by an electric heater. The terminal rotational temperatures for various source temperatures and pressures were determined from an energy balance equation in conjunction with the TOF data. Recently, Pritchard et al. have proposed that the transition probability from the ith to the jth rotational states decreases in proportion to some power of the energy difference between the states. This power law was fitted to experimental results for rotational relaxation in the free jet expansion. The results show that the state‐to‐state rotational relaxation rates vary as the inverse 3/2 power of the energy difference between the initial and final states. The rotational distributions in the jet expa...

Photographic observation of knock with a rapid compression and expansion machine

A new type of rapid compression and expansion machine (RCEM) has been developed, and typical knock scenes were clearly recorded with a high speed laser shadowgraph at a speed of 100,000 frames per second. The RCEM is intended to simulate combustion in an automotive engine. Its piston is driven by an electrohydraulic servo system and is allowed to execute continuous reciprocations up to five times. The combustion chamber is a simple pancake type with an ignition plug on its side and the whole inner view is observable through a glass window on the top.

Fuel Octane and Composition Effects on Efficiency and Emissions in a High Compression Ratio SIDI Engine

The effects of fuel octane have been assessed on the efficiency and emissions of a high compression ratio (e=13) spark ignition direct injection (SIDI) engine. Under low load stratified operation (1200 rpm, ∼20% load), a low octane fuel (RON=84, comprised of toluene, iso-octane, and n-heptane) yielded higher brake thermal efficiency and significantly lower hyd carbon emissions than a base gasoline (RON=91). The indicator diagram for the low octane fuel showed evidence for two stage heat release, suggesting the presence of spark induced compression ignition (SICI). These results suggest that higher efficiency under low load stratified conditions can be obtained with lower octane fuels that undergo SICI combustion. The effect of fuel octane under high load was assessed at WOT with a high RON model fuel (RON=103, comprised of toluene, iso-octane, and n-heptane). This high octane fuel exhibited a torque benefit compared to pure iso-octane (RON=100) and premium gasoline (RON=99) that is significantly greater than expected based on RON alone. The results suggest that a high RON fuel, in particular one that is high in aromatics, yields significant torque benefits under high load.