Principal Component Analysis (PCA) has been of great interest in computer vision and pattern recognition. In particular, incrementally learning a PCA model, which is computationally efficient for large scale problems as well as adaptable to reflect the variable state of a dynamic system, is an attractive research topic with numerous applications such as adaptive background modelling and active object recognition. In addition, the conventional PCA, in the sense of least mean squared error minimisation, is susceptible to outlying measurements. To address these two important issues, we present a novel algorithm of incremental PCA, and then extend it to robust PCA. Compared with the previous studies on robust PCA, our algorithm is computationally more efficient. We demonstrate the performance of these algorithms with experimental results on dynamic background modelling and multi-view face modelling.

A digital particle image velocimetry (PIV) measurement has been carried out to study the large-scale flow characteristics in a single-cylinder engine with a production-type four-valve cylinder head under one intake port deactivation. The measurement plane was located 12 mm below the cylinder head parallel to the flat piston top. Two-dimensional velocity fields from 100 consecutive cycles were acquired at every 30 crank angle interval in the compression stroke to analyse ensemble-averaged mean velocity, cyclic variation of the swirl motion, low-frequency and total velocity fluctuations and their integral length scales. The analysis shows that as one intake port is deactivated, strong swirl forms at the end of the intake stroke and sustains its flow pattern up to the late stage of the compression stroke with the precessing of the swirl centre. Both swirl ratio and swirl centre show significant cyclic variations in the compression process. A low-frequency component with spatial frequency below 0.05 mm-1 (corresponding to a large-scale structure with a spatial scale over 20 mm) is absolutely predominant in the flow field and therefore the low-frequency large-scale flow behaviour determines the basic characteristics of the total in-cylinder flow. The flow field is considerably anisotopic because the integral length scale of any velocity fluctuation components along any direction is different. However, the velocity fluctuation field in the horizontal plane will gradually become homogeneous as the piston moves up in the compression stroke. The integral length scale is in the range of 4-10 mm at an engine speed of 600 r/min. When the engine speed is doubled, flow velocity in the cylinder nearly doubles and velocity fluctuation kinetic energy more than triples though the flow pattern hardly changes.

The fuel distribution and mixture formation processes within an internal combustion (IC) engine can greatly affect its ignition, combustion, pollutant formation, and fuel consumption. For more than two decades the laser-induced fluorescence (LIF) technique has been successfully applied to the study of mixture formation and distribution. However, in a gasoline direct injection (GDI) engine the fuel may exist in either the liquid or vapour phase, and it is therefore advantageous to be able to observe both phases simultaneously. One means of achieving this is the laser-induced exciplex fluorescence (LIEF) technique. This paper details its application to a single-cylinder GDI engine equipped with an air-assisted fuel injection system and full optical access. Naphthalene and N, N-dimethlylaniline (DMA) tracers were used to track the fuel and were excited using the expanded beam from an XeCl excimer laser at 308 nm. An image doubler and optical filtering system was used to collect the images that were recorded from the front of the cylinder. Early and late injection timings were investigated, and the spray characteristics and mixture formation from the two strategies were found to differ considerably. In order to investigate the effect of absorption on the fluorescence signal, the beam was introduced into the cylinder from three directions. Crank angle resolved results, from the start of injection to the end of the compression stroke, are presented, with an image for each illumination direction and injection timing.

A fuel stratification concept is being researched and developed in a three-valve twin-spark ignition engine. This concept requires that two different fuels or fuel components be introduced into the cylinder separately through two independent inlet ports. The fuels will be stratified laterally by means of strong tumble in the cylinder. Similar to the traditional air/fuel stratification engine, this fuel stratification engine can operate in very lean mixture or high exhaust gas dilution at part loads to reduce fuel consumption and NO x emissions. While at high-load operation, a higher compression ratio may be allowed owing to a potential increase in antiknock features if the lower research octane number (RON) fuel or component is ignited first, leaving the higher RON fuel in the end gas region. As a result, the fuel economy can be improved not only at part loads but possibly at full loads as well. This paper reports the development of such a fuel stratification engine. Firstly, the intake system of the engine was modified to produce a strong tumble flow which was measured by a digital particle image velocimetry (PIV) system. Then, a two-tracer planar laser induced fluorescence (PLIF) system was developed to visualize the fuel stratification in the cylinder. The engine combustion at part and full loads was also tested and analysed from cylinder pressure history. These research results show that the present strong tumble flow was characterized by a symmetrically distributed mean velocity in the intake stroke and a very small velocity component along the direction of the tumble rotational axis in the compression stroke. This flowfield created good fuel stratification laterally. The lean burn limit was considerably extended at part loads, and the knock limit at high loads also had a noticeable difference when higher and lower RON fuels respectively were ignited first.

Controlled auto-ignition (CAI) combustion in gasoline engines has great potential for reducing both NO x emissions and fuel consumption, but its application is still hindered by the lack of direct control of combustion phasing and by the limited CAI operation range. In this paper, the effect of injection timing and split injection on CAI combustion is presented in a single-cylinder direct-injection gasoline engine with an air-assisted injector. The CAI combustion was achieved by trapping some of the burned gases within the cylinder by using low-lift short-duration camshafts and early closure of the exhaust valves. During the experiments, the engine speed was varied from 1200 to 2400 r/min and the air-fuel ratio was altered from stoichiometric to the misfire limit. Both single and split injections were investigated at different injection timings and fuel quantities. The experimental results show that injection timing has an important effect on CAI combustion for single and split injections. Early injection produces faster and more stable combustion, less hydrocarbon and CO emissions, but very rapid heat release rates and higher NO x emissions. The CAI operation range could be extended significantly by early injection. Split injection gives even further extension of the CAI range in both stoichiometric and lean mixture operations. These results indicate that optimizing the injection timing and using split injection is an effective way to control and extend CAI operation in a direct-injection gasoline engine.

Tumble motion in the cylinder of a four-valve spark ignition (SI) engine with a production-type cylinder head was studied using cross-correlation digital particle image velocimetry (PIV). The in-cylinder flow field was measured on three planes: the vertical symmetric plane of the combustion chamber, the vertical plane through centres of the intake and exhaust valves, and a horizontal plane 12 mm below the cylinder head. Ensemble-averaged mean velocity, velocity fluctuation distribution and cyclic variation of the instantaneous velocity field were analysed. Analysis results show that the tumble vortex is formed in the early stage of the compression stroke and distorted in the late stage of the compression stroke. The tumble centre is nearly in the centre of the cylinder when the tumble forms. Then it moves gradually to the underneath of the exhaust valves as the piston moves up. It is found that the cyclic variation of the tumble motion at a tumble ratio of 0.9 is so great that the ensemble-averaged flow characteristics hardly represent any individual cycle flow behaviours. Distribution of the velocity fluctuation field is inhomogeneous during the whole compression process. As the engine speed changes the large-scale flow structure seems to remain unaffected.

No abstract