Search Results

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.

Knock in a spark-ignition engine was characterized in terms of its occurrence and magnitude or intensity. Cylinder pressure data from 90 consecutive individual cycles were generated from a single-cylinder engine of disc chamber design at about 72kHz sampling rate over a range of operating conditions between no knock and 100% of the cycles knocking. Mean values and distribution of following parameters were analysed: knock occurrence crank angle, knock intensity, combustion rate and the end-gas thermodynamic state. The effects of fuel octane number and inlet air temperature on these parameters were studied. The thermal imaging technique has been applied to record two-dimensional surface temperatures of cylinder head and piston simultaneously. The change in surface temperatures during knocking and non-knocking cycles was thus studied. As expected, increase in the inlet air temperature or decrease in the fuel octane number caused the knock onset to occur at less advanced spark timing.

The warm-up characteristics of a spark-ignition engine significantly affect fuel consumption and emissions from cars. A thermal imaging technique has been applied to measure the cylinder head surface temperature and piston surface temperature of an internal combustion engine simultaneously. The two-dimensional thermal images of the cylinder head surface temperature were viewed through an infra-red transmitting window mounted in the piston. The piston surface temperature was measured by painting black two small areas of the window's top surface. The similar thermal characteristics of the window material (silicon) to those of a normal piston and good heat transfer between the window and the piston provided realistic operation conditions. The mean and extreme values of the inlet valve, exhaust valve, two other areas of the cylinder head surface and window surface temperatures were measured from the thermal images during the first two minutes of the engine start.

Increasing pressure on lowering vehicle exhaust emissions to meet stringent California and Federal 1993/1994 TLEV emission standards of 0.125 gpm NMOG, 3.4 gpm CO and 0.4 gpm NOx and future ULEV emission standards of 0.04 gpm NMOG, 1.7 gpm CO and 0.2 gpm NOx has focused specific attention on the cold start characteristics of the vehicle's emission system, especially the catalytic converter. From test data it is evident that the major portion of the total HC and CO emissions occur within the first two minutes of the driving cycle while the catalyst is heating up to operating temperature. The use of an electrically heated catalyst (EHC) has been proposed to alleviate this problem but the cost and weight penalties are high and the durability has yet to be fully demonstrated (1)*. This paper describes a method of reducing the light-off time of the catalytic converter to less than 20 seconds by means of an afterburner.