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An experimental investigation has been carried out of the turbulence characteristics of tumble air motion in four-valve pent roof combustion chambers. This was conducted on an optically accessed single cylinder research engine under motored conditions at an engine speed of 1500 rev/min. Four cylinder heads with varying tumble magnitude were evaluated using conventional and scanning Laser Doppler Anemometry (LDA) measurements. Analysis algorithms developed to account for the effects of mean flow cyclic variations and system noise were used to obtain unbiased estimates of turbulence intensity and integral length scales. The cylinder heads were also evaluated for combustion performance on a Ricardo single cylinder Hydra engine. Mixture and EGR loops at 1500 rev/min and 1.5 bar BMEP were carried out and cylinder pressure data was analysed to derive combustion characteristics.

Earlier work has shown that the in-cylinder flow in internal combustion engines can be modelled, with reasonable accuracy, as the sum of an ensemble averaged mean component, a non-stationary ‘turbulence’ component and a ‘cycle-to-cycle’ variation component, the latter being phase-locked to the engine cycles. The development of the LDA technique has enabled direct measurements of the in-cylinder velocity field to be taken, either at a single position in space over the engine cycle, or over a range of spatial positions, at effectively one point in the engine cycle (scanning LDA). Previously, different approaches have been developed for separating the various flow components in the model described above, dependent on the type of data acquired. In this paper a single ‘unified’ method is presented, based on the computation of autocorrelation functions and a completely parametric representation of the various components in the flow model.

To gain a better understanding of the exhaust emissions impact of olefins in a low aromatic, full boiling range gasoline, an evaluation of the before and after catalyst emissions of three highly olefinic refinery streams and three highly paraffinic refinery streams, blended 50/50 in motor alkylate, was conducted using a 3.1 L GM engine. The test fuels were also selected to consider the effects of volatility in addition to olefin concentration. The fuels were evaluated under three steady state engine operating conditions. The results of the tests indicate essentially only small differences in the before and after catalyst total hydrocarbons (THC) between the pairs of highly olefinic streams and the highly paraffinic streams at relatively the same volatility level, for two of the test conditions (2400RPM-light and moderate/heavy loads. The ozone forming potentials (OFP) for these fuels, across all three speed and load conditions, also show relatively small differences.

The development of technology suitable for meeting the CARB Ultra-low- emission-vehicle (ULEV) legislation has now become a main focus for vehicle manufacturers worldwide. This proliferation of interest is mainly a result of the increasing number of eastern US-states currently considering the adoption of CARB legislation and the indication that emission legislation in Europe and Japan for the turn of the century is likely to be of the same severity as CARB ULEV legislation. Current three way catalyst (TWC) emissions control technology suffers from low catalytic conversion efficiency of HC, CO and NOx pollutants during cold operation i.e. before catalyst light off. Cold start emissions generally contribute up to 70% of HC and CO tailpipe emissions during an FTP test. However, in some cases even early light-off of the catalyst, similar to hot operation is not sufficient to achieve catalytic conversion over a test cycle to reach ULEV emissions levels.

Speciated hydrocarbon emissions were measured at steady-state conditions in pre- and post-catalyst exhaust from a modern multi-valve fuel-injected and closed-loop controlled European gasoline engine tested on toluene, isooctane and diisobutylene. Unburned fuel contributed 70-80% of the total engine-out hydrocarbon emissions on toluene, but only 24% and <10% on isooctane and diisobutylene respectively except at idle where values were 71% and 47% respectively. Emissions from both of the aliphatic fuels were dominated by photochemically-reactive olefins such as isobutene and propene, plus ethyne, methane and formaldehyde. With the exception of ethyne, emissions of these compounds were much less from toluene. Even at rich conditions, most hydrocarbons were catalytically controlled to some extent, but the catalyst efficiency was dependant upon hydrocarbon composition.

A scanning Laser Doppler Anemometer system has been developed for the measurement of spatial velocity profiles in motored internal combustion engines. Tests were carried out on a single cylinder engine with a disc shaped combustion chamber, at an engine speed of 1200 rev/min. Ensemble averaged mean and RMS velocity estimates show good agreement with conventional LDA measurements. Longitudinal and transverse autocorrelation functions have been calculated, and estimates have been made of turbulence length scales. These have been found to be comparable with length scales measured in engines by other techniques. This investigation has demonstrated that scanning LDA is a powerful technique for characterising in-cylinder air motion in engines.

An investigation has been carried out to compare the ability of swirling and tumbling flow regimes to enhance the turbulence in a disc-shaped gasoline combustion chamber. Scanning LDA measurements have been made of spatial velocity fluctuations in a high swirl, a tumble and a baseline low swirl build. All of the testwork was carried out under motored conditions at an engine speed of 1200 rev/min. A parametric model has been developed to account for the effects of mean flow cyclic variation and system noise. It is shown that the model fits very well to the experimental data, enabling unbiased estimates of turbulence intensity and turbulence length scale to be made. In the region measured around TDC the high swirl build achieves a uniform increase in turbulence Intensity of about 55% over the baseline build. The tumble build however achieves a peak in turbulence intensity of more than twice the baseline build at 30° BTDC.