Search Results

High resolution planar laser-induced fluorescence (PLIF) measurements were performed in an optically accessible internal combustion (IC) engine to investigate the behavior of scalar dissipation and the fine-scale structures of the turbulent scalar field. The fluorescent tracer fluorobenzene was doped into one of the two intake streams and nitrogen was used as the carrier gas to permit high signal-to-noise ratio fluorescence measurements without oxygen quenching effects. The resulting two-dimensional images allowed for an analysis of the structural detail of the scalar and scalar dissipation fields defined by the mixing of the two adjacent intake streams. High levels of scalar dissipation were found to be located within convoluted, sheet-like structures in accordance with previous studies. The fluorescence data, which were acquired during the intake stroke, were also used to examine the scalar energy and dissipation spectra.

In-cylinder velocity measurements were acquired in a two-valve, single-cylinder research engine to study the bulk fluid motion and small-scale turbulence. Different port geometries (two), different port orientations (two) and both shrouded and non-shrouded intake valves were tested to vary the intake-generated flow. Tests were performed at engine speeds of 300, 600, 900 and 1200 RPM with an atmospheric intake pressure. Prior to testing on the engine, the different head configurations were tested on a steady flow bench. Particle image velocimetry data were taken on a single plane, parallel to the piston surface, in the engine using both a low magnification to characterize the large-scale flow phenomena, and a high magnification to characterize the turbulence field. The low-magnification results showed that the swirl center location was relatively insensitive to engine speed, but did change position throughout the cycle.

Reactivity controlled compression ignition combustion was investigated for three fuel combinations: isooctane-diesel, PRF90-diesel, and E85-diesel. Experiments were conducted at 1200 rpm, 160 kPa absolute intake pressure, and fixed total fuel energy using ‘optimal’ operating condition for each fuel combination that were chosen based on combustion performance from SOI timing and premixed energy fraction sweeps. The heat release duration was found to scale with the difference in reactivity between the premixed and direction injected fuel; a small difference gives rise to short heat release duration, similar to that of HCCI combustion. Conversely, as the difference increases, the heat release period lengthens. The high-speed optical data confirmed that the combustion occurred in a staged manner from the high-reactivity zones, which were located at the periphery of the chamber, to low-reactivity zones in the field of view.

Many combustion researchers use peak pressure rise rate or ringing intensity to indicate combustion noise in lieu of microphone data or using a combustion noise meter that simulates the attenuation characteristics of the engine structure. In this paper, peak pressure rise rate and ringing intensity are compared to combustion noise using a fully documented algorithm similar to the ones used by combustion noise meters. Data from multiple engines operating under several low-temperature combustion strategies were analyzed. The results suggest that neither peak pressure rise rate nor ringing intensity provides a direct correlation to engine noise over a wide range of operating conditions. Moreover, the estimation of both metrics is often accompanied by the filtering of the pressure data, which changes the absolute value of the results.

A novel algebraic similarity model for subgrid scalar dissipation rate has been developed as part of the Large Eddy Simulation (LES) package KIVA3V-LES for diesel engine study. The model is proposed from an a priori study using Direct Numerical Simulation (DNS) of forced isotropic turbulence. In the a posteriori test, fully resolved turbulent passive scalar field measurements are used to validate the model in actual engine flows. For reason of the length limit by SAE and the specific interest in engine applications, only a prior test and a posteriori test in engine flows are included in this paper. A posteriori tests in isotropic cube flow, turbulent round jet and flame cases will be presented in separate papers. An engine LES simulation of multi consecutive cycles was performed in this study.

The effects of fuel composition on homogeneous charge compression ignition (HCCI) combustion were studied experimentally in an engine employing negative valve overlap (NVO). Three test fuels, varying in ignition quality and volatility, were investigated for their effect on engine performance and combustion phasing; comparisons were made to a full-run 87-octane base fuel. The three test fuels, which varied in research octane number from 69 to 98, were all found to advance the combustion timing slightly relative to the base fuel, suggesting some differences in the ignition chemistry. The combustion performance at a fixed combustion phasing, however, was found to be comparable, within the limits of the system, for all of the fuels. A major testing issue that limited the system repeatability was the formation of combustion chamber deposits under some operating conditions. A methodology to mitigate these effects was employed with some success.

The light-medium load operating range (4-7 bar net IMEP) presents many challenges for advanced low temperature combustion strategies utilizing low cetane fuels (specifically, 87-octane gasoline) in light-duty, high-speed engines. The overly lean overall air-fuel ratio (Φ≺0.4) sometimes requires unrealistically high inlet temperatures and/or high inlet boost conditions to initiate autoignition at engine speeds in excess of 1500 RPM. The objective of this work is to identify and quantify the effects of variation in input parameters on overall engine operation. Input parameters including inlet temperature, inlet pressure, injection timing/duration, injection pressure, and engine speed were varied in a ~0.5L single-cylinder engine based on a production General Motors 1.9L 4-cylinder high-speed diesel engine.