Colin P. Garner

Thermo-Mixed Hydrodynamics of Piston Compression Ring Conjunction

A new method, comprising Navier–Stokes equations, Rayleigh–Plesset volume fraction equation, an analytical control-volume thermal-mixed approach and asperity interactions, is reported. The method is employed for prediction of lubricant flow and assessment of friction in the compression ring–cylinder liner conjunction. The results are compared with Reynolds-based laminar flow with Elrod cavitation algorithm. Good conformance is observed for medium load intensity part of the engine cycle. At lighter loads and higher sliding velocity, the new method shows more complex fluid flow, possessing layered flow characteristics on the account of pressure and temperature gradient into the depth of the lubricant film, which leads to a cavitation region with vapour content at varied volume fractions. Predictions also conform well to experimental measurements reported by other authors.

Barrel swirl breakdown in spark-ignition engines: Insights from particle image velocimetry measurements

Abstract Particle image velocimetry (PIV) has been used here to study the formation and breakdown of barrel swirl (‘tumble’) in a production geometry, four-stroke, four-valve, motored, spark-ignition, optically accessed internal combustion (IC) engine. The barrel swirl ratio (BSR) of the cylinder head could be enhanced by means of a port face inducer gasket so that the flow processes taking place at low and high swirl ratios could be investigated conveniently. Double-exposed images from planes both parallel and perpendicular to the cylinder axis were recorded at selected crank angles through the induction and compression strokes at a motored engine speed of 1000 r/min, with a wide open throttle, for both high and low BSR cases. The recorded images were interrogated by digital autocorrelation to give two-dimensional maps of instantaneous velocity. In both high and low BSR cases, a barrel or tumbling vortex motion is generated during induction, which is shown to persist throughout the majority of the compression stroke. The details of barrel swirl formation during induction and its subsequent modification during compression, however, differ strongly between the two cases. These differences can be explained qualitatively in terms of two main events; the first being competition during induction between vortices of unequal strength and the second being competition between the large-scale swirl motion and the local flow field generated by piston motion during compression. In the low barrel swirl case, significant dissipation occurs owing to these interactions and consequently the large-scale motion exhibits lower mean velocities and undergoes significant distortion. In the case of high BSR, the competition effects are minimized and a single ordered vertical vortex exhibiting high velocity magnitudes is observed to avoid piston induced distortion. It then moves into the apex of the pent roof combustion chamber where it survives as a single ordered vortex until at least 40° crank angle (CA) before top dead centre (TDC). Limitations and developments of the PIV technique are discussed.

Unthrottled engine operation using variable valve actuation: the impact on the flow field, mixing and combustion

The effect on the intake flow field, air fuel mixing processes, thermodynamic performance and emissions output has been investigated for a range of valve operating profiles. A standard speed load point of 2000 rpm and 2.7 bar IMEP720° has been reached by throttling the intake whilst running standard cam profiles, by early closing of both inlet valves (EIVC) and by early closing of each inlet individually to generate bulk swirl motions within the cylinder. Data has been recorded at stoichiometric air fuel ratios for both direct injection and port fuelled operation. The valve profiles have been applied to two single cylinder homogeneous gasoline direct injection (GDI) spark ignition engines, developed to investigate the potential of controlling engine load by limiting the inducted air mass using fully variable valve timing (FVVT) to reduce pumping losses at part load. The first engine featured a full length optical liner, allowing 2D Particle Image Velocimetry (PIV) measurements of the intake flow fields to be made, along with Mie imaging studies of the liquid fuel fraction. The second was a thermodynamic engine equipped to measure specific fuel consumption and emissions of CO2, CO, NOX and THC. The work shows that fuel economy benefits can be gained by operating the engine with unthrottled EIVC operation. However, the interaction between the intake air and direct injection fuel spray means performance is highly dependant upon which valve is operated and the timing of the direct injection fuel spray. Copyright

An investigation of string cavitation in a true-scale fuel injector flow geometry at high pressure

String cavitation has been studied in an optical automotive size fuel injector with true-scale flow geometry at injection pressures of up to 2050 bar. The multihole nozzle geometry studied allowed observation of the hole-to-hole vortex interaction and, in particular, that of a bridging vortex in the sac region between the holes. A dependency on Reynolds number was observed in the formation of the visible, vapor filled vortex cores. Above a threshold Reynolds number, their formation and appearance during a 2 ms injection event was repeatable and independent of upstream pressure and cavitation number.

Direct measurements of burning velocity of propane-air using particle image velocimetry

The main objective of this communication is to demonstrate the application of particle image velocimetry (PIV) to the direct measurement of burning velocity in a constant-volume combustion chamber. PIV was used to measure the unburned gas velocity field ahead of the flame front. By means of simultaneous measurement of local flame propagation speed with a pair of ionization probes, the laminar burning velocity of propane-air mixtures initially at atmospheric pressure P = 101.3 kPa and temperature T = 298 K was also measured for equivalence ratios in the range 0.7 {le} {phi} {le} 1.4. The measured values are compared with other published results.

Simultaneous Study of Intake and In-Cylinder IC Engine Flow Fields to Provide an Insight into Intake Induced Cyclic Variations

Simultaneous intake and in-cylinder digital particle image velocimetry (DPIV) experimental data is presented for a motored spark ignition (SI) optical internal combustion (IC) engine. Two individual DPIV systems were employed to study the inter-relationship between the intake and in-cylinder flow fields at an engine speed of 1500 rpm. Results for the intake runner velocity field at the time of maximum intake valve lift are compared to incylinder velocity fields later in the same engine cycle. Relationships between flow structures within the runner and cylinder were seen to be strong during the intake stroke but less significant during compression. Cyclic variations within the intake runner were seen to affect the large scale bulk flow motion. The subsequent decay of the large scale motions into smaller scale turbulent structures during the compression stroke appear to reduce the relationship with the intake flow variations.

Big End Bearing Losses with Thermal Cavitation Flow Under Cylinder Deactivation

The paper presents a mixed thermo-hydrodynamic analysis of elliptic bore bearings using combined solution of Navier–Stokes, continuity and energy equations for multi-phase flow conditions. A vapour transport equation is also included to ensure continuity of flow in the cavitation region for the multiple phases as well as Rayleigh–Plesset to take into account the growth and collapse of cavitation bubbles. This approach removes the need to impose artificial outlet boundary conditions in the form of various cavitation algorithms which are often employed to deal with lubricant film rupture and reformation. The predictions show closer conformance to experimental measurements than have hitherto been reported in the literature. The validated model is then used for the prediction of frictional power losses in big end bearings of modern engines under realistic urban driving conditions. In particular, the effect of cylinder deactivation (CDA) upon engine bearing efficiency is studied. It is shown that big-end bearings losses contribute to an increase in the brake specific fuel consumption with application of CDA contrary to the gains made in fuel pumping losses to the cylinders. The study concludes that implications arising from application of new technologies such as CDA should also include their effect on tribological performance.

The Effects of Exhaust Back Pressure on Conventional and Low-Temperature Diesel Combustion

Modern diesel engines are seeing increasing system and after-treatment complexity which can lead to significant increases in the exhaust back pressure (EBP). This increases the amount of trapped residuals, raising the charge temperature but reducing the oxygen concentration. In this work, these effects of the EBP on diesel engine performance and emissions under conventional and low-temperature diesel combustion (LTC) regimes were investigated. Increasing the EBP resulted in higher pumping work for both combustion modes. While for conventional diesel combustion the effect of the EBP on combustion and emissions were not significant, for LTC the higher back pressures influenced the combustion and emissions formation processes. At low-load conditions, the increase in the charge temperature advanced combustion; at intermediate-load conditions, the reduction in the oxygen concentration delayed it. Smoke emissions were significantly reduced by a higher back pressure at intermediate-load conditions.

Particle image velocimetry measurements of in-cylinder flow in a multi-valve internal combustion engine

Particle image velocimetry (PIV) has been used here to characterize the formation and breakdown of barrel swirl or tumble in a production geometry, four-stroke, four-valve motored optical internal combustion (IC) engine. The engine was motored at 1000 r/min at wide open throttle. Double exposed images were recorded from a plane parallel to the cylinder axis which passed through the centre-lines of an inlet and exhaust valve. Particle image velocimetry images from a range of crank angles between inlet valve closure and the ignition point were interrogated by digital autocorrelation to give two-dimensional maps of instantaneous velocity. The in-cylinder flow is characterized by the formation of an ordered barrel swirl or tumbling vortex, which is shown to persist throughout the majority of the compression stroke with maximum velocities of the order of three times the mean piston speed and a high velocity bulk flow at the time of ignition near the spark plug. With respect to the PIV technique itself, image labelling and cross correlation are considered essential to improve measurement dynamic range, valid data rate and tolerance to velocity gradients in the turbulent flows encountered near top dead centre (TDC).

The effects of split injections on high exhaust gas recirculation low-temperature diesel engine combustion

Diesel engine emissions of oxides of nitrogen and smoke can be reduced simultaneously through the use of high levels of exhaust gas recirculation to achieve low-temperature combustion. However, single fuel injection per cycle diesel low-temperature combustion is also characterized by high fuel consumption and high total unburned hydrocarbons and carbon monoxide emissions. This work focuses on investigating the potential of a split (50/50) main fuel-injection strategy to reduce smoke, total unburned hydrocarbons and carbon monoxide emissions at exhaust gas recirculation levels lower than those required to achieve single-injection diesel low-temperature combustion at a medium-load, medium-speed operating condition. Experiments were performed on a 0.51 l single-cylinder high-speed direct-injection diesel engine running at 1500 r/min at an operating condition corresponding to a gross indicated mean effective pressure of 500 kPa. At this load, exhaust gas recirculation levels of 62% are needed to realize near-zero nitrogen oxide and smoke emissions, but this leads to an unacceptable reduction in thermal efficiency as well as high total unburned hydrocarbons and carbon monoxide emissions. This work compares the effects of split fuel injections at an exhaust gas recirculation level of 52% by volume to those from single injections at exhaust gas recirculation levels of 52% and 62%. The results demonstrate that the combined effects of exhaust gas recirculation rate and split injections can achieve near-zero nitrogen oxide with good thermal efficiency and total unburned hydrocarbons and carbon monoxide emissions much lower than at 62% exhaust gas recirculation. Single injection at this point results in excessive smoke, which can be reduced by over 75% through the split-injection strategy. These results are particularly relevant as they demonstrate very low nitrogen oxide emissions from an engine operation with acceptable thermal efficiency and at practical exhaust gas recirculation levels.