Optical and Numerical Investigations of Flame Propagation in a Heavy Duty Spark Ignited Natural Gas Engine

Increasing the natural gas (NG) use in heavy-duty engines is beneficial for reducing greenhouse-gas emissions from power generation and transportation. However, converting compression ignition (CI) engines to NG spark ignition operation can increase methane emissions without expensive aftertreatment, thereby defeating the purpose of utilizing a low carbon fuel. The widely accepted explanation for the low combustion efficiency in such retrofitted engines is the lower laminar flame speed of natural gas. In addition, diesel engine’s larger bowl size compared to the traditional gasoline engines increases the flame travel length inside the chamber and extends the combustion duration. However, optical measurements performed in this study suggested that a fast-propagating flame was developed inside the cylinder even at extremely lean operation. This was supported by a three-dimensional numerical simulation, which indicated that the squish region of the bowl-in-piston chamber generated a high turbulence intensity inside the bowl. However, the flame propagation experienced a sudden 2.25x reduction in speed when transiting from the bowl to the squish region. Such a phenomenon was caused by the large decrease in the turbulence intensity inside the squish region during the combustion process. Moreover, the squish volume trapped an important fuel fraction, and it is this fraction that experienced a slow and inefficient burning process during the expansion stroke. This resulted in increased methane emissions and reduced combustion efficiency. Overall, it was the specifics of the combustion process inside a bowl-in-piston chamber not the methane’s slow laminar flame speed that contributed to the low methane combustion efficiency for the retrofitted engine. The results suggest that optimizing the chamber shape is paramount to boost engine efficiency and decrease its emissions.

Analisa Pengaruh Penggunaan Bahan Bakar Diesel Like Fuel dan Minyak Solar Terhadap Unjuk Kerja Multi Swirl Combustion System (MSCS) Piston Chamber pada Small Marine Diesel Engine

Produksi minyak dunia diperkirakan telah mencapai puncaknya pada tahun 2000, ini berarti bahwa eksplorasi minyak bumi sudah maksimal dan selanjutnya akan mengalami penurunan. Ini akan menyebabkan dalam kurun waktu 20 tahun produksi minyak dunia akan kembali seperti pada tahun 1980-an(OPEC ,2009). Di lain pihak ketergantungan terhadap minyak bumi pada waktu yang sama akan terus meningkat akibat pertambahan penduduk dan kegiatan industri dan pembangunan. Akibat dari hal ini adalah harga energi yang semakin tinggi dan pasokan minyak yang menurun. Hal ini dapat dirasakan dari naiknya harga minyak mentah dan dicabutnya subsidi harga bahan bakar minyak oleh pemerintah Indonesia. Pada penelitian ini peneliti tertarik pada minyak solar dari oli bekas(Diesel – Like Fuel) di gunakan sebagai bahan bakar pada motor diesel dengan menggunakan Multi Swirl Combustion System (MSCS) Piston Chamber. Penelitian ini dilakukakan untuk mengetahui unjuk kerja dari motor diesel Multi Swirl Combustion System (MSCS) Piston Chamber saat menggunakan bahan bakar solar dari daur ulang minyak pelumas bekas(Diesel – Like Fuel) dan minyak solar(Pertamina Dex) sebagai pembanding. Metode yang digunakan dalam melakukan penelitian ini adalah metode eksperimental. Pengujian dilakukan dengan melakukan eksperimen pada variasi bahan bakar. Lalu akan dilakukan pengamatan terhadap unjuk kerja dari motor diesel yang digunakan untuk melakukan penelitian ini. Parameter unjuk kerja yang akan diamati adalah daya motordan BSFC. Dari hasil analisa terhadap daya motor diesel PE(Watt) penggunaan MSCS Piston Chamber pada beban 1000 Watt, 1500 Watt, dan 2000 Watt, nilai PE(Watt) pertamina dex lebih tinggi dari Diesel – Like Fuel/DLF sebesar rata – rata 9,86 %, 10,09 %, dan 10,32 %. Dari hasil analisa terhadap BSFC penggunaan MSCS Piston Chamber pada beban 1000 Watt, 1500 Watt, dan 2000 Watt, BSFC pertamina dex lebih rendah dari Diesel – Like Fuel/DLF sebesar rata – rata 6,36 %, 8,98 % dan 13,26 %. Dapat ditarik kesimpulan berdasarkan BSFC dan daya motor(PE) penggunaan bahan bakar minyak solar(Pertamina Dex) lebih ekonomis dibandingkan dengan minyak solar dari oli bekas(Diesel – Like Fuel)

Two-Stage Lean-Burn Combustion Inside a Natural-Gas Spark-Ignition Engine With a Bowl-in-Piston Chamber

The conversion of existing diesel engines to spark ignition (SI) operation by adding a low-pressure injector in the intake manifold for fuel delivery and replacing the original high-pressure fuel injector with a spark plug to initiate and control the combustion process can reduce U.S. dependence on petroleum imports and increase natural gas (NG) applications in heavy-duty transportation sectors. Since the conventional diesel combustion chamber (i.e., flat-head-and-bowl-in-piston-chamber) creates high turbulence, the converted NG SI engine can operate leaner with stable and repeatable combustion process. However, existing literatures point to a long late-combustion duration and increased unburned hydrocarbon emissions in such retrofitted engines that maintained the original combustion chamber. Consequently, the main objective of this paper was to report recent findings of NG combustion characteristics inside a bowl-in-piston combustion chamber that will add to the general understanding of the phenomena. The new results indicated that the premixed NG burn inside the bowl-in-piston combustion chamber will separate into a bowl-burn and a squish-burn processes in terms of burning location and timing. The slow burning event in the squish region explains the low slope of the burn rate towards the end of combustion in existing studies (hence the longer late-combustion period). In addition, the less-favorable conditions for the combustion in the squish region explained the increased carbon monoxide and unburned hydrocarbon emissions.

Optofluidic lens based on electrowetting liquid piston

The conventional electrowetting lens usually has one tunable liquid-liquid (L-L) interface. The shape of L-L interface is deformed to get variable focal length due to electrowetting effect. However, contact angle saturation of the L-L interface is an unavoidable problem which prevents focal length from further changing. Here, we demonstrate an optofluidic lens based on electrowetting liquid piston. The proposed lens has two connected chambers, the piston chamber and the lens chamber to form a closed-loop fluidic system. The electrowetting liquid piston can generate clockwise and counter-clockwise liquid flows, which can make the L-L interface convex and concave. To prove the concept, we fabricate an optofluidic device whose shortest negative and positive focal lengths are ~−17.9 mm and ~18 mm with 5 mm aperture, respectively. The proposed optofluidic lens has large tunable focal length range. Widespread application of such an adaptive lens is foreseeable.

The Theoretical Volumetric Displacement of a Check-Valve Type, Digital Displacement Pump

This paper has been written to develop closed-form equations for describing the theoretical displacement of a check-valve type, digital displacement pump. In theory, the digital displacement pump is used to alter the apparent volumetric displacement of the machine by short circuiting the flow path for reciprocating pistons within the machine that would ordinarily deliver a full volumetric flow rate to the discharge side of the pump. The short circuiting for the pistons is achieved by opening and closing a digital valve connected to each piston chamber at a desired time during the kinematic cycle for each reciprocating piston. Experience with these machines has shown that the expected volumetric displacement for the machine tends to decrease with pressure. This paper presents a theoretical explanation for the reduced volumetric displacement of the pump and quantifies the expected behavior based upon the digital valve command, the residual volume of fluid within a single piston chamber, and the fluid bulk modulus-of-elasticity. In summary, it shown that the apparent volumetric displacement of the machine may be reduced by as much as 10% for high-displacement commands and by as much as 30% for low-displacement commands.

Study of the Dynamic Characteristics of Piston Chamber Pressure and its Optimizing

In order to develop a new type of high-performance axial piston pump, the impact of the dynamic response characteristics of piston chamber pressure to the stability of cylinder block were analyzed. This paper a new type of valve plate which combined two fixed throttling grooves with a triangular groove (called three-level gain) was put forward so as to reducing the excessive pressure adjustment of the dynamic response of piston chamber pressure and improving the stability of cylinder block. The simulation results indicate that not only the cavitation is reduced, but also the stability of the dynamic response of piston chamber pressure is remained at various swash plate angle which makes it applicable to variable piston pump. The results also indicate that the flow pulsation of variable displacement pump is significantly decreased in different operating conditions.

Research on Influence Factors of Hydraulic Support Moving Velocity in Coal Mining Based on AMESim

In view of the high efficiency modernization coal demand, in this paper, the hydraulic support moving velocity influence factors were studied. Building simulation model of the thrust jack of hydraulic support with the simulation software AMESim, and run the simulation. Comparing the simulation results by setting different parameters value. It is concluded that the rated flow of pump station and hydraulic controlled check valve opening quantity will affect the speed of hydraulic support moving frame. This result provides reference for the optimal design of hydraulic support and improving the efficiency of coal mining. Key words: Moving velocity of hydraulic support; Rated flow; Hydraulic controlled check valve; AMESim 1 Tntroduction In the process of coal mining,the movement of hydraulic support needs in a timely manner with coal mining progresses, thrust jack plays a vital role for the movement of the hydraulic support. Therefore, it is very meaningful to research the influence factors of hydraulic support moving velocity With thrust control loop as the breakthrough point . 2 The working principle of the thrust control loop The movement of the hydraulic support and push the slide are achieved by thrust jack. Thrust jack is located in the middle part of the base of the hydraulic support, its end hinged with the base of the hydraulic support, the other end is connected with flexible scraper conveyor. When the hydraulic support moving, uninstall first, then the hydraulic controlled check valve make high pressure liquid into the piston rod cavity of thrust jack, the liquid in piston chamber flow back. At the same time, make thrust jack cylinder to move forward with the support of conveyor, thus, the whole hydraulic support is pulled to the coal wall, to complete the move. when pushing the slide, make high pressure liquid into the piston chamber , the liquid in piston rod cavity flow back, and, make the piston rod out with the support of hydraulic support. so,the conveyor is pushed to the coal wall,it is completed.