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A fast response NO detector has been developed to study fast transient emissions from internal combustion engines. The device combines the standard ChemiLuminescence Detector (CLD) measurement technique used in conventional NO detectors with the rapid sampling system of an existing Fast Flame Ionisation Detector (FFID) hydrocarbon detector. The 10-90% response time of the fast NO detector is approximately 3 milliseconds and enables resolution of transient NO concentration within individual engine cycles. Both the fast NO and fast HC detectors were fitted in the exhaust port of a firing SI engine. With the probe tips at the same position, simultaneous fast transient NO and HC concentration data have been recorded during steady state and transient engine load conditions. Cycle-by-cycle NO concentration, HC concentration, and cylinder pressure are compared and features of the transient NO and HC concentration are discussed.

A fast-FID sampling technique has been developed to study top-land crevice out-gassing from the moving piston of an SI engine. A sampling probe, housed in the piston crown, delivered gas to the FID head via a flexible transfer tube. Comparisons of the HC concentrations at the top-land location and the bulk gas above the piston crown confirm that HC material is out-gassed from the top-land region during the expansion stroke and is followed by more rapid out-gassing after EVO. The removal of wall HCs has been detected during the exhaust stroke from the probable scrolling effect produced by the rising piston scraping unburned material from the cylinder wall.

The action of crevices in an operating SI engine has been studied with a fast-FID. A single-cylinder Ricardo E6 research engine was fuelled with propane and operated at 1300 RPM. FID measurements in the exhaust port have shown that advancing the ignition timing from 30°BTDC (MBT) to 60°BTDC raises the HC concentration by 25% during the first 120°CA of the exhaust stroke and by 20% for the remainder of the stroke. A static “artificial” crevice of known volume, mounted inside the engine cylinder was used to study the differing HC outgassing characteristics at the two ignition timings. When sampling in-cylinder at the mouth of this crevice, the opposite effect of a 50% reduction in outgas HC concentration occurred when the ignition was advanced to 60°BTDC. It is argued that advancing the ignition causes earlier enflamement of the static crevice and induces burned as well as unburned gas to enter the crevice thereby diluting the HCs from this source.

A fast-response FID has been used to study the concentration of hydrocarbon material at four different locations in a firing SI engine. These were: on the flat surface of the cylinder head, at the exhaust valve seat crevice, just downstream of the exhaust seat in the exhaust port and 20mm downstream from the valve stem in the exhaust manifold. A close-fitting sleeve arrangement enabled the sample tube to be positioned accurately flush with the head face and also to be slid away from the wall into the bulk gases whilst maintaining a gas-tight seal. In this way, wall effects could be noted by moving the probe position without stopping the engine and directly comparing with hydrocarbon levels in the bulk gas. Using propane in a fully-warmed up engine, results showed the presence of HCs residing in a 2mm layer adjacent to the wall after EVO and during the exhaust stroke. These could be detected flowing over the valve seat after EVO and were also observed at the manifold location.

Hydrocarbon wall quenching has been studied using a 19mm diameter, 1m long combustion tube, open at one end. Mixtures of propane, heptane, iso-octane and gasoline, initially quiescent, were burnt with the ignition source at the closed end. The post-flame HC levels were measured at a series of axial locations using a fast FID. The results indicate that the effective quench layer thickness increases significantly as the molecular weight of the fuel is increased. The diffusion/mixing time constant of the quench layer was found to be approximately 0.1s for propane, 0.4s for iso-octane and 1.0s for gasoline. The axial variation of residual HC levels suggests that flame stretch is a factor influencing the extent of the quench layer.