Performance and emission evaluations of a prototype stepped-piston engine using carburetor and direct fuel-injection systems

Two-stroke engines have been used for sometimes in automotive and stationary applications since early 20th century. The advantages of two-stroke engines are obvious, i.e., lighter, simpler and less expensive to manufacture. Technically, two-stroke engines have the potential to pack almost twice the power into the same space because there are twice as many power strokes per revolution. The combination of lightweight and twice the power gives two-stroke engines a great power-to-weight ratio compared to many four stroke engine designs. However due to the short-circuiting process of the fuel before combustion, this has resulted in deterioration in overall performances especially poor combustion efficiency and high white smoke emission problem. Coupled with the improvement in the four-stroke engine technology, the former has overcome the latter in being the choice for mobile platform applications. Due to high fuel cost and the need to explore the use of other fuel sources, notably gaseous fuels, a number of enthusiasts and engine developers have revisited the two-stroke engine design. Fuels such as hydrogen and methane are said to be ideal for use with the incorporation of the some new features (Goldsborough and Blaringan, 2003). An engine design and development program was initiated at Universiti Teknologi Malaysia (UTM) in year 2003 to develop local R&D capabilities in small power-train engineering. The exercise evolved around the development of an air-cooled single cylinder of stepped-piston engine concept. The term “stepped piston” refers to the conventional piston having compounded with a larger diameter section at the rear section of its geometry. The changes to the original design were made as the research group feels that there are rooms for improvements. In addition to this, the modifications will infuse other innovative scope of work from design to product testing activities (Hooper, 1985).This program, eventually leads to the incorporation of features, is expected to enhance performance of the prototype and subsequently exhaust emission. This is in anticipation of producing a working prototype for multiple applications namely stationary and automotive. The gasoline stepped-piston engine is a relatively new design concept for small mobile power plants. It is an engine, operating on a two-stroke cycle but is infused with four-stroke engine features. It has a build-in supercharger mechanism (by virtue of the extended flange) that improves the scavenging process thus improve combustion efficiency. Due to these operating characteristics, the engine has all the attributes of a low emission, high-efficiency power plant that eliminates many of the major weaknesses associated with the Otto four-stroke engine and with modern two-stroke engines

Development of a reduced multi-component chemical kinetic mechanism for the combustion modelling of diesel-biodiesel-gasoline mixtures

In this study, a compact combined reaction mechanism for diesel-biodiesel-gasoline mixtures (CDBG) is developed, comprising n-heptane, methyl butanoate (MB) and methyl decanoate (MD) as well as toluene and isooctane to represent the combustion characteristics of diesel, biodiesel and gasoline fuels, respectively. The mechanisms are separately reduced prior to combining by means of directed relation graph (DRG), directed relation graphs with error propagation (DRGEP) and full species sensitivity analysis (FSSA). The reduced mechanisms are then combined, and extensive validations are carried out for closed homogenous reactor application under the following conditions: T = 600–1700 K, P = 1–50 atm, and equivalence ratios (Φ) of 0.25–1.5 (156 setups in total). To boost the accuracy of the CDBG mechanism, cross-reaction analysis is performed to identify the important intermediate species and reactions. The identified species and reactions are subsequently integrated into the CDBG mechanism, resulting in significant improvements in ID timings up to 30%, 18% and 16% for the CDBG sub-mechanisms of diesel, biodiesel and gasoline, respectively. In addition, Arrhenius rate constant optimisation is also employed to further improve the ignition behaviour of the proposed kinetic mechanism. The results revealed that the dual implementation of the cross-reaction analysis and Arrhenius rate constant optimisation diminished the maximum associated errors considerably, down to 14.6%, 16.9% and 14.9% for the CDBG sub-mechanisms of diesel, biodiesel and gasoline, respectively. Concisely, the best results achieved at T = 600–1700 K were P = 41 atm and Φ=1, P = 1,4 atm and Φ=1, and P = 50 bar and Φ=0.3 for diesel, biodiesel and gasoline surrogates, respectively

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Enhancing the performance of a 125 cc single-cylinder, aircooled, gasoline two-stroke engine

A unique stepped-piston engine was developed by a group of researchers at UTM. The development work engulfs design, prototyping and testing over a predetermined period of time. The aim is to demonstrate environmental-friendly capability producing comparable output with low-fuel consumption. In its carbureted version, it incorporates a three-port transfer system and a dedicated crankcase breather. These features will enable the prototype to have high induction efficiency and to behave very much a two-stroke engine but equipped with a four-stroke crankcase lubrication system. In the final stage of development it was subjected to a series of laboratory trials. It was also tested on a small watercraft platform with promising indication of its flexibility of use as a prime mover in mobile platform. In an effort to further enhance its technology features, the researchers have embarked on the development of an addon auxiliary system. The system comprises of an engine control unit (ECU), a direct-injector unit, a dedicated lubricant dispenser unit and an embedded common rail fuel unit. This support system was incorporated onto the engine to demonstrate the finer points of environmental-friendly and fuel economy features. The outcome of this complete package is described in the paper, covering the methodology and the final characteristics of the mobile power plant

Development of a reduced multi-component chemical kinetic mechanism for the combustion modelling of diesel-biodiesel-gasoline mixtures

In this study, a compact combined reaction mechanism for diesel-biodiesel-gasoline mixtures (CDBG) is developed, comprising n-heptane, methyl butanoate (MB) and methyl decanoate (MD) as well as toluene and isooctane to represent the combustion characteristics of diesel, biodiesel and gasoline fuels, respectively. The mechanisms are separately reduced prior to combining by means of directed relation graph (DRG), directed relation graphs with error propagation (DRGEP) and full species sensitivity analysis (FSSA). The reduced mechanisms are then combined, and extensive validations are carried out for closed homogenous reactor application under the following conditions: T = 600–1700 K, P = 1–50 atm, and equivalence ratios (Φ) of 0.25–1.5 (156 setups in total). To boost the accuracy of the CDBG mechanism, cross-reaction analysis is performed to identify the important intermediate species and reactions. The identified species and reactions are subsequently integrated into the CDBG mechanism, resulting in significant improvements in ID timings up to 30%, 18% and 16% for the CDBG sub-mechanisms of diesel, biodiesel and gasoline, respectively. In addition, Arrhenius rate constant optimisation is also employed to further improve the ignition behaviour of the proposed kinetic mechanism. The results revealed that the dual implementation of the cross-reaction analysis and Arrhenius rate constant optimisation diminished the maximum associated errors considerably, down to 14.6%, 16.9% and 14.9% for the CDBG sub-mechanisms of diesel, biodiesel and gasoline, respectively. Concisely, the best results achieved at T = 600–1700 K were P = 41 atm and Φ=1, P = 1,4 atm and Φ=1, and P = 50 bar and Φ=0.3 for diesel, biodiesel and gasoline surrogates, respectively

Review of the advances in integrated chemical kinetics-computational fluid dynamics combustion modelling studies of gasoline-biodiesel mixtures

Biodiesel combustion in diesel engines is associated with reduced carbon monoxide, particulate matter and unburned hydrocarbons emissions, but several concerns remain including carbon deposition, low thermal efficiency and elevated nitrogen oxides production. To this end, the incorporation of gasoline additive has been proposed as a solution to the drawbacks posed by biodiesel. Integrated chemical kinetics-computational fluid dynamics combustion modelling is a widely used tool to understand the combustion characteristics of new fuel mixtures. This study provides a thorough review of the advances gained in the field of combustion modelling for gasoline-biodiesel mixtures. A thorough appraisal of gasoline surrogate mechanisms such as the primary reference fuel, toluene primary reference fuel and multi-component mechanisms is presented. Developments in the biodiesel surrogate mechanisms such as methyl-butanoate, methyl-hexanoate, methyl-heptanoate, methyl-octanoate, and methyl-decanoate are also discussed. Furthermore, this study also presents a wide-reaching analysis of the modelling results looking into the effects of gasoline addition on the combustion characteristics of gasoline-biodiesel mixtures. From the modelling studies reviewed, the addition of gasoline brings about an increase in the ignition delay timing, in-cylinder pressure and heat release rate (at high temperatures). Also, the rise in gasoline fraction (at low temperatures) leads to the reduction in the combustion duration, nitrogen oxides and soot emissions, but increased carbon monoxide and hydrocarbons emissions. Finally, increased gasoline fraction improves the fuelling economy (at high temperatures) and the combustion stability (at low temperatures)