Opposed-piston Engines Research Articles

Effect of injection strategy on spray and combustion processes in 2-stroke rod-less opposed piston engine (2S-ROPE)

The 2-stroke Rod-less Opposed Piston Engine (2S-ROPE) is a novel engine design that has garnered attention owing to its high power and low fuel consumption. This study investigated the effects of different fuel injection strategies on the in-cylinder working process of a 2S-ROPE engine, which features a smaller combustion space and lateral injection than conventional diesel engines. A high-precision three-dimensional simulation model was developed to examine the fuel atomization and in-cylinder combustion processes under four distinct injection strategies (S1, S2, S3, and S4). The results demonstrated that the injection strategy significantly influenced the number of oil droplets, particularly for small particles. The number of small droplets in S4 was approximately 6 times that in S1. The double-layer injection strategies (S3 and S4) exhibited a better atomization breakup and oil-air mixing, leading to a faster combustion rate and higher lift power than the single-layer injection strategies (S1 and S2). These findings suggest that the double-layer injection strategy is more suitable for a 2S-ROPE engine, increasing the lift power by up to 23 %. The results can guide the improvement of combustion parameters in most opposed piston engines.

Study on the influence principle and application law of intake wall thickness on uniflow scavenging opposed-piston engine

Energy efficient utilization is an important research direction of energy conversion systems. Uniflow scavenging opposed-piston engine has the potential to achieve higher thermal efficiency than classic engines. The lack of valve mechanism leads to the poor scavenging performance of uniflow scavenging opposed-piston engines. Many studies have been conducted to improve scavenging performance by optimizing intake structure. However, the critical influence of intake wall thickness has not been considered. Therefore, a three-dimensional simulation model of intake wall thickness was established and validated. Then the detailed influence of intake wall thickness was explored. Last, the influence law of intake wall thickness under different application conditions is explored. According to the simulated results, intake wall thickness significantly affects the scavenging process by influencing exhaust gas backflow and changing the scavenging passage; the vital influence of intake wall thickness should be considered in optimizing other intake structures. Thicker intake wall thickness increases the backflow resistance and retains more exhaust gas backflow in the intake port, which is conducive to orderly cleaning backflow exhaust gas. The thinner intake wall thickness should be selected at small intake pressure, and the thicker intake wall thickness should be selected at large intake pressure.

Effect of swirl-spray impact on the comprehensive performance of uniflow-scavenging opposed-piston engines

Uniflow-scavenging opposed-piston (USOP) engines exhibit high thermal efficiency and power density. However, the USOP engine has a continuous in-cylinder airflow state between different cycles, which affects direct injection oil spray distribution. The USOP engine nozzles were mounted on a cylinder liner. The forward and reverse impacts of the in-cylinder swirl differed in the asymmetric orifice layout. A dual-intake channel USOP simulation model was established. The key parameters of the simulation model were verified, and the effects of forward and reverse impacts under different nozzle layouts and swirl strengths were analysed by simulation. The results show that all swirl-spray impacts benefit the combustion. Swirl-spray impacts can effectively improve the oil spray distribution and atomisation. In addition, reducing the swirl in the next cycle concentrates the exhaust gas in the cylinder centre, improving the scavenging efficiency. Forward and reverse impacts enhance and weaken the in-cylinder swirl, respectively. However, the effect of the reverse impact was more pronounced than that of the forward impact.

Effects of multitype intake structures on combustion performance of different opposed-piston engines

The uniflow scavenging opposed-piston (USOP) engine has more potential for performance improvement than the conventional engine. The combustion performance of the USOP engine is greatly affected by the uniflow scavenging process. However, the uniflow scavenging process fluctuates greatly. In addition, the opposed free piston linear generator (OFPLG) and the opposed-piston two-stroke (OP2S) belonging to the USOP engine have different piston motion laws, so the influence of intake structure on different USOP engines should be explored. This study established and verified a CFD simulation model and selected three optimization directions (intake swirl, scavenging performance, and exhaust gas backflow inhibition). The effects of intake wall thickness, intake port shape, intake port offset, and the number of intake ports were investigated by an orthogonal test. Last, three optimum schemes that respond to the three optimization directions were used to compare the combustion performance of different USOP engines. Results showed that the intake wall thickness, intake port shape, and intake port offset significantly affect the combustion performance. Improving the intake swirl and scavenging performance are effective methods to optimize comprehensive performance. Intake swirl regulation improves combustion performance by accelerating the uniform distribution of oil spray. Scavenging performance optimization improves combustion performance by increasing the in-cylinder fresh air mass. Intake wall thickness and intake port offset can simultaneously improve the intake swirl and scavenging performance.

Recent Advances in Opposed Piston Engines for Ultralow Emissions

Over the last several years, the development and demonstration of opposed-piston (OP) engines has advanced rapidly. This paper presents results of the Heavy Duty Diesel Demonstration Program, funded by the California Air Resources Board, that provide evidence a diesel OP engine can achieve ultralow levels of tailpipe NOx while also reducing fuel consumption (and CO2 emissions) compared to a reference vehicle using a modern, conventional diesel engine. It is important to note that the OP engine achieved these results using only conventional, underfloor aftertreatment systems. No additional emissions control technologies were required.

Development of a 4 stroke spark ignition opposed piston engine

Abstract The purpose of this project was to develop a low-cost OP engine, 4-stroke, gasoline by joining two single-cylinder reciprocating internal combustion engines with side valves on the block, removing the heads. The chosed engine was Model EY15 of Robin America. Joining these two engine blocks together made possible to build an opposed-piston engine (OPE) with two crankshafts. In this new engine, the combustion chamber is confined to the space inside the cylinder between the piston heads and the chamber between the valves. The pistons move in the cylinder axis in opposite directions, a feature typical of opposed-piston engines. After building the engine, parameters characteristic of the OPE, such as: rotational speed, torque, fuel consumption and emissions, were measured on an Eddy currents dynamometer. With the collected data, power, specific consumption and overall efficiency were calculated, allowing to conclude that the motor with the opposed-piston configuration is less expensive and is more powerful. The development of the opposed-piston engine in this project has shown that it is feasible to build one engine from a different one already in use, reducing the manufacturing and development costs. In addition, higher power can be obtained with better specific fuel consumption and less vibration.

Experimental test stand for development of an opposed-piston engine and initial results

The article presents the reason for developing a 0D predictive and diagnostic model for opposed-piston (OP) engines. Firstly, a description of OP engines, together with their most important advantages and challenges are given together with current research work. Secondly, a PAMAR-4 engine characteristic is presented. After that the proposed 0D predictive model is described and compared with the commercially availible software. Test stand with most important sensors and solutions are presented. After that the custom Engine Control Unit software is characterized together with a 0D diagnostic model. Next part discusses specific challenges that still have to be solved. After that the preliminary test bed results are presented and compared to the 0D simulations. Finally, the summary together with possible future improvement of both 0D predictive model and test bed capabilities are given.

The closed-cycle model numerical analysis of the impact of crank mechanism design on engine efficiency

The research presents a review and comparison of different engine constructions. Investigated engines included crankshaft engines, barrel engine, opposed-piston engines and theoretical models to present possible variations of piston motion curves. The work comprises also detailed description of a numerical piston engine model which was created to determine the impact of the cycle parameters including described different piston motion curves on the engine efficiency. Developed model was equipped with Wiebe function to reflect a heat release during combustion event and Woschini’s correlation to simulate heat transfer between the gas and engine components.Various scenarios of selected engine constructions and different working conditions have been simulated and compared. Based on the results it was possible to determine the impact of different piston motion curves on the engine cycle process and present potential efficiency benefits.

Unsteady conjugated heat transfer in cylinder of highly loaded opposed-piston engine

Paper presents a method of calculating the temperature distribution in cylinder for a 2-stroke, opposed-piston (OP) internal combustion engine (ICE). Development of such machines has been very limited after World War II due to technological and ecological problems [9], therefore progress in numerical modeling for analyzing highly boosted OP engines was also halted. Current technology permits returning to the OP arrangement, where due to better combustion chamber shape it is potentially possible to achieve higher thermodynamic efficiency than in arrangement with the cylinder head [9, 10]. Authors decided to use a general purpose CFD-program (in this case Ansys Fluent) coupled with additional tools to calculate conjugated heat transfer between the load in the cylinder and the cylinder itself to get a 3D temperature distribution in solid body.

An Opposed-Piston Diesel Engine

Typical conventional diesel engine designs are based on arrangements of single piston and cylinder sets placed sequentially either in-line or offset (“V”) along the crankshaft. The development of other engines, such as the opposed piston type, has been motivated by potential advantages seen in such designs, which may not be viable in conventional in-line or V engine arrangements. Several alternatives to conventional engine design have been investigated in the past and some aspects of these designs have been utilized by engine manufacturers. The design and development of a proof-of-concept opposed piston diesel engine is summarized in this paper. An overview of opposed-piston engines is presented from early developments to current designs. The engine developed in this work is a two stroke and uses four pistons, which move in two parallel cylinders that straddle a single crankshaft. A prechamber equipped with a single fuel injector connects the two cylinders, forming a single combustion chamber. The methodology of the engine development process is discussed along with details of component design. Experimental evaluations of the assembled proof-of-concept engine were used for determining feasibility of the design concept. An electric dynamometer was used to motor the engine and for loading purposes. The dynamometer is instrumented for monitoring both speed and torque. Engine parameters measured include air flow rate, fuel consumption rate, inlet air and exhaust temperatures, and instantaneous cylinder gas pressure as a function of crank position. The results of several testing runs are presented and discussed.

Calculation of the thermoelastic state of cylinders of opposedpiston engines

Calculation of the thermoelastic state of cylinders of opposedpiston engines

Some Early Experiences of Mechanical Vibration in Marine Engine Systems

Everything which is struck rings; everything has a particular ring.—Pythagoras of Samos (582-507 B.C.) The lecture is divided into the following sections. Introduction. Early days. Camshaft drives. Camshaft drive at free end and after end of crankshaft; later developments. Mass balancing of internal-combusion engines. Single-piston assemblies; unbalanced centrifugal and inertia forces. Mass balancing opposed-piston engines. Ship vibration; scavenge-crank balance weights; scavenge-pump reciprocating parts; crankshaft-coupling-bolt failures; change of firing order; results and conclusions from vibration tests. Differential-stroke (mass-balanced) opposed-piston engines; first fully balanced opposed-piston engines; lever-driven scavenge pumps. Transverse (rolling) vibration of engine frame. Experimental determination of the natural frequency of transverse (rolling) vibration of opposed-piston engines; transverse vibration of engine frame in twin-screw ships and its control. Torsional vibration. Investigation of side-connecting-rod failures; investigation of torsional vibration; retiming the crankshaft system; general; marine steam reciprocating engine. Devices for controlling torsional vibration. Tuned and damped vibration absorbers; dynamic vibration absorbers in opposed-piston-engine propulsion systems; Bibby peripheral grid springs; vibration absorbers at free ends of crankshafts; experimental absorber with peripheral helical springs; Doxford-Bibby absorber. Later history. Large six-cylinder opposed-piston engines; alternative viscous-friction dampers; modified vibration absorber; stiffer crankshafts; P-type engines; J-type engines.