A new internal combustion engine configuration: opposed pistons with crank offset

[Abstract]: Theoretical and experimental performance results for a new internal combustion engine configuration are presented in this paper. The engine is a piston ported, spark ignition petrol engine which consists of two opposed pistons in a single cylinder controlled by two synchronously timed crankshafts at opposite ends of the cylinder. It makes use of crank offset to create the required piston motion aimed at engine efficiency improvements through thermodynamic performance gains. In particular, the engine employs full expansion in which the power stroke displaces a larger volume than the compression stroke, thereby allowing the expanding gas to reach near atmospheric pressure before the exhaust port opens. This allows more work to be done by each thermodynamic cycle. It also features a greater rate of volume change after combustion than a convention 4-stroke engine for the same crank speed. This reduces the time that the temperature difference between the gas and the cylinder is high relative to a conventional engine which in turn, should reduce the heat lost from the combustion products. Thermodynamic and friction modelling of the engine indicated that efficiencies around 38% might be achieved. However, experiments with a prototype engine demonstrated that friction losses in the engine exceeded that predicted in the original modelling

Absolute concentration measurements of OH* in an axisymmetric hydrogen-air premixed flame adjacent to a hot graphite model

Absolute concentration of the chemiluminescent radical OH* was determined in an axisymmetric hydrogen-air premixed flame adjacent to a resistively-heated graphite surface. Two-dimensional images of the axisymmetric chemiluminescence from the excited-state of OH were recorded by an ICCD camera with a narrow-band filter at approximately 310 nm. A temperature of around 1800 K was achieved on the graphite surface using an electrical heating power of 5.5 kW. Surface temperatures were measured using a two-color ratio pyrometry (TCRP) technique. The line-of-sight-integrated chemiluminescent emissions that were imaged using the ICCD device were transformed to radial distributions through an Abel inversion method. A new method for calibration of the absolute number density of the radiating radical OH* is proposed based on the intensity ratio of the measured OH* chemiluminescence and the radiation emitted from the hot graphite surface. This is a convenient approach in the present work because adequate signal magnitudes from both these phenomena are acquired by the ICCD device simultaneously during testing

Hardware-based engineering problem solving for on-campus and external teams

We contend that engineering analysis and design will continue to rely on the synthesis of experimental observations and theoretical analyses. For the past three years, we have been providing teams of on-campus and external students the opportunity to work with actual engineering hardware as a focus for engineering analysis and problem solving. Providing external teams of student with the opportunity to problem solve with actual engineering hardware represents a number of challenges. By focusing on initial value problems and requiring the teams to design the parameters necessary to achieve the desired system performance, we have been able to expose both on-campus and external teams to problem solving with testable physical systems and actual engineering hardware

A study to identify relationships between the grade given for an undergraduate problem solving course and the students' reported satisfaction levels

[Abstract]: Data for an undergraduate problem solving course was collected from 92 external students and 73 on campus students. Student satisfaction levels were assessed from feedback submitted with the assessment. An email-based survey was completed on a voluntary basis by a portion of the students after completing one further semester of study. The data collected in the survey suggests that reported satisfaction levels have no discernible correlation with grades awarded for each student. The subject consisted of two assignments and a final examination. The data from feedback included in assignment submissions was assessed using inferential analysis and compared with reported satisfaction levels from the voluntary responses to the email-based survey. Indications were found that respondents who indicated dissatisfaction also reported no benefit from participation in the course with respect to improved capability to work in a team or benefits accrued in the course for use in later subjects

Student views on hardware-based problem solving activities for external and on-campus teams

[Abstract]: Hardware-based problem solving activities for teams of on-campus and external students have been introduced in a third level problem solving course over the past 3 years. The problems typically involve the teams in the acquisition and analysis of genuine data, the development and implementation of models for the hardware performance, and the testing of their solutions on the hardware. However, such activities are resource-intensive and it was not clear if the students shared our enthusiasm for hardware-centric problem solving. We have sought such evidence from the students through feedback and survey tools. It appears that the students’ perspectives on hardware-based problem solving are closely aligned with ours and that their interest in the course is enhanced by the hardware-based approach

Air motor for improved engine brake efficiency: design and preliminary experiments

The brake efficiency of a throttled internal combustion engine is reduced at low load operation because of the engine work required to drop the intake manifold pressure. These throttling losses are experienced by all throttled engines operating at less than wide open throttle (WOT). By replacing the throttle plate with a suitable air motor, work can be recovered in an expansion process that reduces the induced air pressure to the same intake manifold pressure as the throttled engine. To maximize the benefits from coupling the air motor to the engine cycle, the air should be returned to a thermal state identical to that of the throttled case at some point prior to combustion. This might be achieved either: (i) prior to cylinder compression via regenerative heat transfer to the inducted air; or (ii) through cylinder compression at an increased compression ratio. The work generated by the Induction Air Motor (IAM) can be directly applied to the engine output thereby increasing the brake efficiency for the same indicated work. This paper reports on the performance of an IAM designed to reduce intake pressure of an engine for low load operation. Increased brake efficiency will be achieved. The IAM design specifications are explored using a numerical model including isentropic efficiency, friction and service life considerations. A prototype has been constructed and was bench tested at flows and pressures comparable to a throttled engine. These tests indicated that the modelled friction was lower than the friction measured during the experiments. From the experiments performed with the prototype, the net performance of an IAM will give efficiency improvements in excess of 5% for an equivalent throttled engine operating at loads in the range up to 10% of its WOT power

A comparison between two-position variable compression ratio and continuously variable compression ratio engines using numerical simulation

Fuel consumption for the New European Driving Cycle (NEDC) is assessed via numerical simulation for a vehicle operating with two types of variable compression ratio device: i) a continually variable compression ratio (VCR) device that optimises efficiency at all loads, and ii) a VCR device that allows the engine to operate at one of two discrete compression ratios. The simulated engine configuration uses late intake valve closing (LIVC). A maximum geometric compression ratio (GCR) of 17:1 is adopted in the simulations resulting in a constant effective compression ratio of 10.2:1 in all configurations. Reduction from full load is achieved in the simulation with LIVC until the maximum GCR is reached after which lower loads are achieved through throttling. In the two-position VCR engine simulation, the full load range is achieved through throttling in combination with LIVC. At part load, in combination with LIVC, the VCR devices increase the geometric compression ratio to return the effective compression ratio to that for full load in each case. The simulations indicate that the increase in net fuel consumption over a driving cycle is effectively no different for the two-position VCR engine relative to a continually variable CR and this justifies further research into two-position VCR technology. Net fuel consumption can also be improved by the use of a limited acceleration that maintains the engine in the reduced compression stroke configuration. An acceleration rate with a driver feedback mechanism is proposed which, in combination with a two-position VCR engine, shows potential for significant reduction in fuel consumption of greater than 15% relative to the full compression, fixed CR configuration for the NEDC

Computational and experimental investigation of using an extractor in a vertical gravitational flash tank separator

A vertical gravitational flash tank separator can be used to increase the performance of a refrigeration cycle. Using the vertical gravitational flash tank separator improves the effective area and enhances the heat transfer coefficient inside the evaporator. However, the vertical gravitational flash tank separator still needs further investigation to improve its performance. This paper provides an investigation study to demonstrate the improvement of separation efficiency using an extractor inside the vertical gravitational flash tank separator. Computational Fluid Dynamic (CFD) was used to assess the optimum configuration and dimension of the extractor. A series of experiments were performed to test and confirm the proposed CFD configuration of the extractor design. The results revealed that the extractor had increased the separation efficiency by 2 %. The CFD simulations gave a good agreement with the experiments; however, all the simulations underestimated the liquid separation efficiency by approximately 0.02 over the range of conditions tested

Detached eddy simulation of an adjustable radial ejector

A high-performance Adjustable Radial Ejector (ARE) might be capable of achieving optimum performance over a wide range of operating conditions by changing the primary nozzle and ejector duct throat areas during operation by altering the separation of the disk-like surfaces. Previous results show that the simulations of a prototype radial ejector using a variety of RANS turbulence models have not achieved consistently good agreement with the experimental data across the range of ejector operating conditions. The present work describes new simulations of an ARE using Detached Eddy Simulation (DES) in ANSYS FLUENT in conjunction with the DES k-ω SST turbulence model. The influence of varying both the nozzle throat separation (d = 0.39, 0.49 and 0.59 mm) and the duct throat separation (D = 2.3, 2.6, 3.0 and 3.5 mm) on the performance of an ARE is assessed for different operating conditions. The results show that smaller nozzle separations increase the entrainment ratio, but decrease the critical back pressure. Larger duct separations do not always increase the entrainment ratio, but do always yield a lower critical back pressure

Measurement of turbulent supersonic steam jet flow characteristics using TDLAS

Ejectors have no moving parts and are preferable to mechanical compressors in many applications, but ejectors typically have a relatively low efficiency. To aid in the ejector design process, thorough understanding of the turbulent mixing of multi-phase compressible jets is beneficial. This paper reports experimental results for Tunable Diode Laser Absorption Spectroscopy (TDLAS) measurements derived from an axisymmetric supersonic steam jet apparatus. In this experimental work, a supersonic steam jet nozzle exit of a diameter 13.6 mm was surrounded by a low-speed flow of dry nitrogen. The TDLAS system was traversed through the flow at three different planes downstream from the ejector nozzle exit: 15, 20, and 30 mm distance. At each of the three planes, line-of-sight measurements were made with the laser passing through locations between 0 and 15 mm from the jet centreline. Through the analysis of the TDLAS data and application of the Abel inversion method, the radial distribution of the pressure, temperature, and the concentration of the water-vapour were obtained. The key findings are that it is possible to determine key physical parameters using experimental TDLAS measurements when combined with a suitable numerical optimization approach