Small Two-Stroke Engine Research Articles

The effect of muffler design on reducing the noise pollution of a small two-stroke engine

Designing an efficient muffler for single-cylinder IC engines is not an easy task due to the limitation in designing a large muffler and the possibility of engine suffocation. In this regard, this research aims to experimentally investigate the feasibility of inexpensive muffler modification of a small portable two-stroke engine to reduce noise pollution. In experiments, the default muffler as a control treatment and a modified muffler together with a redesigned muffler have been examined to investigate the effect of muffler internal geometry and muffler design on sound emission characteristics. Based on the obtained results, the sound pressure level (SPL) of the modified and redesigned mufflers decreased by 5.31 and 6.86 percent compared to the default muffler, respectively. Meanwhile, installing the modified and redesigned mufflers increased the transmission loss (TL) equal to 8.62 % and 10.08 % compared to the default muffler, respectively. Also, the outcome of Discrete Fourier Transform (DFT) revealed that the intensity and amplitude of output frequencies from the redesigned muffler was significantly reduced in the frequency range of 2–6 kHz. As a general conclusion of this study, by installing the redesigned muffler, the maximum working times of the operator increased by 12.1 h at 5000 rpm.

A Preliminary Study of Spark-Ignition System for Free-Piston Linear Engine

In recent years, the free-piston linear engine (FPLE) has attracted increasing interest from researchers worldwide. With the development of computer control technology, internal combustion engine technology, and material science, there have been significant advances in the aspects of FPLE simulation, experimental techniques, as well as systems FPLE control. This paper presents a model of a two-stroke, spark-ignition free-piston engine converted from two small two-stroke engines. It has a bore size of 34 mm and a maximum stroke of 28 mm. The linear engine uses gasoline fuel that is available on the market. The purposes of the research show a model of the starting system, investigation the effects of spark timing, and effective pressure. A premixed air-fuel charge is conducted by a carburetor then it is directly supplied into each cylinder. The spark timing was varied at 1 mm and 2 mm away from the maximum top dead center with the speed starting at 10 Hz. The model successfully ignited with a maximum pressure of 7.5 kg/cm2 at the ignition of 1 mm before top dead center (TDC) and 9.5 kg/cm2 at the ignition of 2 mm before TDC. The research has completed the initial intentions such as a theoretical investigation, calculation, determination of the engine model, and starting mechanism. Preliminary results have confirmed the feasibility of proposing the FPLE model.

Study of Scavenging and Combustion Processes for Small Two-Stroke Aviation Heavy Fuel Direct Injection Engines

Heavy-fuel aviation piston engines (HF-APEs) are widely used in general aviation and unmanned aerial vehicle (UAV) due to their safety and fuel economy. This paper describes a numerical and experimental study of scavenging and combustion processes on a 2-Stroke Direct Injected HF-APEs for light aircraft, with its cylinder specifically designed as cross scavenging. A 3-Dimentional transient model of in-cylinder flow and combustion process is established by the Forte platform, and the engine test system is set up. By comparing the simulation results to the experimental results, it showed that multi-ports cross scavenging can generate unbalanced aerodynamic torque in the cylinder. In the compression process, the swirl ratio (SR) gradually increases, and the peak SR reaches 15. Moreover, approximately 25% of exhaust residual gas in the cylinder is conducive to the fuel atomization and evaporation process in a high-altitude environment. When the injection timing is between −8 °CA and −16 °CA, the engine has the optimal power and economy performance at different altitudes. Finally, when the injection advance angle moves forward by 4 °CA, the maximum pressure increases by 2 MPa, with the rising rate decreasing gradually. The results have important significance for the development of the combustion system of small 2-Stroke Direct Injected HF-APEs.

Modeling of two-stroke aviation piston engines for control applications

Two-stroke Aviation Piston Engines are multivariable systems with severe non-linear dynamics, making their modeling challenging for control engineers. Although many studies have been conducted on simplified modeling of four-stroke gasoline engines and large-scale two-stroke diesel engines for automobiles and ships, only a few have focused on the general modeling of small two-stroke aviation engines. Thus, extensive research on a general modeling method for two-stroke aviation engines is required. A general non-linear Mean Value Engine Model (MVEM) of two-stroke aviation piston engines is developed. Various parts of the model are represented by appropriate empirical equations that require little engine data and easily fit different engines. The objective is to develop a general and accurate method for rapid engine modeling that captures the main dynamics and can create control systems for two-stroke aviation piston engines. The model is validated using HIRTH-3203 and NU-57 measurement data, and the results show that the issues of fitting simplicity and general applicability are well addressed. Finally, the air-fuel ratio control based on the model predictive control method is carried out on the HIRTH-3203 MVEM, which demonstrates the effectiveness of the proposed MVEM in the controller design and evaluation. The proposed model may support the application of new control technologies, such as adaptive control and intelligent control, in the two-stroke aviation piston engine systems.

Feasibility study on the conversion of a small engine into a single-piston expander operating under different pressure and valve timing conditions

There are limited studies on improving the piston expander performance for a wider operating range by adopting the variable valve timing method. This study uses a simple conversion technique to develop a single-piston expander (SPE) from a small two-stroke engine. The SPE is being tested at different operating conditions to study the feasibility of the SPE operating under different intake pressure and valve timing conditions. By fixing the exhaust valve timing, the SPE was tested at four intake pressure; 3, 4, 5, and 6 bar, while the intake valve closing varied from 30° to 110°. From the study, the highest power produced by the SPE was only 64 Watt when tested at 6 bar, with the intake valve opening at TDC and closed at 70°. The results show that the converted SPE is feasible in terms of functionality, but it is not performance-wise because much power has been lost through the recompression process. The study also observed that the intake valve timing could significantly affect the SPE power output, besides the intake pressure alone.

Comparison of fuel consumption and emission of small two-stroke engine of electric generator fuelled by methanol, biogas, and mixed methanol-biogas

A two-stroke engine run with flexible fuel of biogas or methanol is not established yet. It is the objective of this work to provide 2 stroke engine for an electric generator that can be run by using flexible fuels namely: methanol, biogas, and mixed methanol-biogas. A small single cylinder 2 stroke engine of an electric generator was set to be able to be fuelled by using 3 different types of fuel namely biogas (50% vol. CH4, 15% vol. CO2, 0 ppm H2S), methanol (CH3OH) with 97% vol. purity and mixed biogas-methanol. The electric generator that is used is for providing 750-watt electricity. The compression pressure was around 10 Bar with cylinder volume around 63 cc. The engine was set with an easy switch system of fuel. Since methanol is used as one type of fuel that is used, then special lubricant should be prepared for this purpose. It is generally known that commercial synthetic lubricant that is usually used and mixed with gasoline for 2-stroke engines is found not well mixed with methanol. The castor oil is selected to be used as a lubricant to be mixed with methanol with a ratio of methanol to castor oil of 50:1. During using only biogas as a fuel, the castor oil was dripped around 3 drops/minute in the biogas-air mixer chamber. The emission, as well as fuel consumption, were investigated both in idle position and loaded at 200 watts. It is found that for only biogas fuel, the fuel consumption is 18.83 L/minute and increases to become 15, 17 L/minute at a load of 200 watts. By using only methanol as a fuel, the fuel consumption is found 0.009 L/minute and increases to become 0.011 during loading at 200 watts. If mixed fuel is applied the biogas consumption becomes 2.06L/minute in idle position and 4.43 L/minute at a load of 200 watts. The lowest CO emission in idle position was found with biogas as fuel at 0.18 % vol., followed by mixed fuel biogas+ methanol at 0.26% vol. and the highest is methanol fuel at 0.25%vol. for a load of 200 watts, the lowest CO emission is found the same at biogas fuel at 0.18% vol., followed by mixed biogas + methanol at 0.011 % volume, and the worst is found for methanol fuel with CO emission of 0.33 % vol.

Development of a methodology for calculating the working process of a small-size two-stroke internal combustion engine

On the basis of the available theoretical calculations, methods for calculating the working process and power characteristics of internal combustion engines and the experimental studies carried out, a method for calculating the working process for small-sized two-stroke internal combustion engines was developed and tested. In the course of this work, the following results were obtained: the parameters of the working process and power characteristics of a small two-stroke internal combustion engine; the parameters obtained by calculation during the study of the Evolution 20GX2 engine were compared with the results of an experimental study. According to the results of the comparison, deviations in the values of the parameters of the engine under study from the results of the experimental study at the maximum power and maximum speed modes were identified.

Performance Enhancement Using Different Nitromethane Blends in a Small Two-Stroke Engine

Abstract Nitromethane being immiscible in gasoline is often added to methanol to enhance the engine power output. But with the use of methanol as the base fuel, the brake specific fuel consumption (BSFC) of the spark ignition (SI) engine often doubles due to its lower heating value. To constrain this increase to a marginal value, a tri-component fuel blend consisting of nitromethane-alcohol-gasoline was prepared and observed to be stable. Methanol, ethanol, and butanol were the chosen alcohols for the tests due to their popularity as alternate fuels for SI engines. Tests on a small (35cc) two-stroke SI engine revealed that the torque produced with the use of tri-component blends was comparable with nitromethane-methanol blend and was on an average 1.35 times higher than gasoline. However, the BSFC with the nitromethane-butanol-gasoline blend was 50% lower than nitromethane-methanol blend and was only 14% higher than gasoline. The emission analysis showed lower HC emissions with the tri-component blends proving the improved combustion efficiency due to better mixing of the fuel-air mixture. Combustion analysis showed the increased heat release rate with nitromethane addition due to its higher flame speeds.

Jet ignition in small two-stroke engines: an experimental survey on benefits and challenges

Increasingly stringent policy on carbon dioxide have proved to be a severe constraint on the design of light two-stroke (2S) engines. The enhancement of efficiency is claimed to be the main target to make these devices compliant with future regulations. Low-Pressure Direct Injection (LPDI) was found to be effective in the reduction of fuel short circuit, thus improving efficiency and mitigating pollution. Innovative combustion technologies are required to exploit further the fuel potential. Jet Ignition (JI), i.e., ignition provided by means of hot turbulent jets, was found to improve the fuel ignition process, leading to a faster and more uniform combustion. Several benefits are shown in over forty years of Literature, from the higher performance to wider flammability limits. However, few studies have been performed on small 2S engines, for which only full-load data are available. This paper aims at experimentally evaluating benefits and challenges of adopting the JI technology on light 2S LPDI engines at both full- and low- load operation. Different configurations of passive prechambers have been investigated in terms of indicated cycle, brake efficiency and cycle-to-cycle variation. A sensitivity analysis on the spark timing was performed to fine-tune the combustion process. Results show the adequacy of the JI for use in devices operating close to full torque, like garden tools; however, issues related to the excessive amount of residual gas or to the rapid pressure decrease during the expansion phase were highlighted. Different solutions for solving these challenges are proposed.

소형 2행정 엔진의 전송 포트 형상에 따른 소기 성능에 대한 수치 해석적 연구

소형 2행정 엔진의 전송 포트 형상에 따른 소기 성능에 대한 수치 해석적 연구

A Practical Design Approach to Improve the Charging Efficiency of a Small Two-Stroke High Speed Engine Based on Basic CFD

The paper deals with the optimisation of the charging efficiency in a small two-stroke high-speed engine according to well-established design guidelines. The aim is to present the method successfully used in the preliminary screening of the performance improvement attainable in a crank-case-compression engine by design modifications to the transfer ports and manifolds. The method applies a basic CFD model of the steady-state flow across the cylinder block validated against experimental tests at the discharge flow bench. This model is used to approximate the actual scavenging process through a transient simulation of the cold flow across the cylinder inside which the piston is fixed at the bottom centre. A fast assessment of the charging efficiency is permitted by a transported passive scalar implemented in the model to easily estimate all the parameters needed for monitoring the effectiveness of the scavenging process at each crankangle. This practical design approach has been applied to the geometry of a Schnürle-type loop-scavenged 125cc single-cylinder engine compliant with the 2018 FIA homologation form for the KF2 karting competition category. The maximum increase of indicated mean effective pressure expected according to the comparison between the CFD simulations of the original and the modified design of the transfer ports is approximately equal to 4%. This result demonstrates that the CFD analyses are sensitive to the limited modifications commonly needed to tune two-stroke racing-engines and confirms that the suggested design approach can be profitably employed by engineers and technicians involved in the design of small two-stroke highspeed engines.

The Control Space for Knock Mitigation in Two-Stroke Engines for 10–25 kg Remotely Piloted Aircraft

Interest is growing in converting commercially available, two-stroke spark-ignition engines from motor gasoline to low-anti-knock-index fuel such as diesel and Jet A, where knock-limited operation is a significant consideration. Previous efforts have examined the knock limits for small two-stroke engines and explored the effect of engine controls such as equivalence ratio, combustion phasing, and cooling on engine operation during knock-free operation on high octane number fuel. This work culminates the research begun in those efforts, investigating the degree of knock-mitigation achievable through varying equivalence ratio, combustion phasing, and engine cooling on three small (28, 55, and 85 cm3 displacement) commercially available two-stroke spark-ignition engines operating on a 20 octane number blend of iso-octane and n-heptane. Combustion phasing had the largest effect; a 10 deg retardation in the CA50 mass-fraction burned angle permitted an increase in throttle that yielded a 9–11% increase in power. Leaning the equivalence ratio from 1.05 to 0.8 resulted in a 10% increase in power; enriching the mixture from 1.05 to 1.35 yielded a 6–7% increase in power but at the cost of a 25% decrease in fuel-conversion efficiency. Varying the flow rate of cooling air over the engines had a minimal effect. The results indicate that the addition of aftermarket variable spark timing and electronic fuel-injection systems offer substantial advantages for converting small, commercially available two-stroke engines to run on low-anti-knock-index fuels.

Experimental Investigation of Fuel Anti-Knock-Index Requirements in Three Small Two-Stroke Engines for Remotely Piloted Aircraft

Small remotely piloted aircraft (10–25 kg) that are powered by internal combustion engines typically operate on gasoline with an anti-knock index (AKI) > 80. To comply with the single-battlefield-fuel initiative [Department of Defense (DoD) Directive 4140.25], interest has increased in converting power plants for these platforms to run on low-AKI fuels such as diesel and Jet-A with AKIs of ∼20. It has been speculated that the higher losses (short circuiting, incomplete combustion, heat transfer) that cause these engines to have lower efficiencies than their conventional-scale counterparts may also relax their required fuel AKI. The fuel-AKI requirements of three two-stroke spark ignition (SI) engines with 28, 55, and 85 cm3 displacements were mapped, and the performance was compared to that on 98 ON (octane number) fuel. Switching from 98 ON fuel to 20 ON (Jet-A and diesel equivalent AKI) fuel while maintaining optimum combustion phasing led to a 3–5 crank-angle degree (CAD) reduction in burn angle, a 2–3% increase in power, and a 0.5–1% (absolute) increase in fuel-conversion efficiency at non-knock-limited conditions through shortening of the CA0–CA10 burn angle. The efficiency improvement translates to a 6% increase in range or endurance. The results indicate that abnormal combustion is not a significant obstacle to operating small commercial-off-the-shelf (COTS) engines on low-AKI fuels and that most of the power and efficiency improvements demonstrated in previous heavy-fuel conversion efforts were the result of modifications made to accommodate low-volatility fuels, not the faster burn rate of the low-AKI fuels themselves.

Performance Enhancement of a Small Two-Stroke Engine Using Nitromethane Blends

Increasing demand for unmanned aerial vehicles (UAVs) calls for a better understanding of its propulsion system. The present study characterizes a small two-stroke glow plug engine for up to 10 kg class of UAVs. To enhance the specific power output of the engine, nitromethane was used as a fuel additive. Understanding the effect of nitromethane concentration on the engine characteristics is the key objective of this present study. An engine test rig has been built to test a small two-stroke engine. The engine was run at various equivalence ratios. Engine characteristics such as thrust, RPM, torque, power, brake-specific fuel consumption (BSFC), and brake thermal efficiency (BTE) have been measured and compared with the base methanol fuelled engine. The results show around a 24% rise in the engine thrust with 40% (by mass) of nitromethane addition to methanol fuel. Energy balance analysis was carried out to show that the increased thrust is due to enhanced combustion efficiency with nitromethane addition. Hence, it is proposed that nitromethane blends can be used in short bursts whenever a large thrust is required by the UAV.

2행정 소형엔진의 대기오염물질 배출특성에 관한 연구

2행정 소형엔진의 대기오염물질 배출특성에 관한 연구

Cylinder Tribology in Small Two-Stroke Engine Using the Methanol Fuel (Comparison between Engine Test and Sliding Test)

Recently, the issue of resources drying up and environmental problems have become more and more serious, and interest has been growing in methanol as an alternative fuel. As a result, in this paper, the cylinder tribology in a small two-stroke engine using methanol fuel and gasoline fuel was studied. An experiment was conducted with an engine and simulated sliding equipment. After the operation was repeated at regular time intervals, the amount of wear of the cylinder wall was investigated. Results show that the wear for methanol fuel was smaller than that for gasoline fuel. To investigate the difference why, the viscosity and Thermo Gravimetry (TG) properties of oils on the cylinder walls were analysed. Simulated sliding tests to imitate the engine case to test lubrication conditions were also carried out. Methanol fuel shows higher viscosity and lower friction due to sustaining the oil film on the cylinder wall. The reduced wear with methanol fuel measurements could be obtained.

305 小型2ストロークエンジンのシリンダーとリング間のトライボロジー特性 : ガソリン燃料とメタノール燃料の比較(機械要素・設計工学II)

305 小型2ストロークエンジンのシリンダーとリング間のトライボロジー特性 : ガソリン燃料とメタノール燃料の比較(機械要素・設計工学II)

Direct Fuel Injection of LPG in Small Two-Stroke Engines

The commonly used carburetted two-stroke engines in developing countries have high exhaust emission and poor fuel efficiency. To meet more rigid emissions requirements, two-stroke vehicles are typically phase out in favour of four-stroke engines. The problems of ubiquitous legacy two-stroke vehicles remain unsolved by these measures and they are likely to be a major source of transport for many years to come. A number of technologies are available for solving the problems associated with two-stroke engines such as catalytic after-treatment and direct fuel injection (DI). However, these solutions are relatively high cost and have shown only slow market acceptance for applications in developing countries. Research in recent years has demonstrated that direct fuel injection is a well developed and readily deployable solution to existing two-stroke engines. Gaseous fuels such as Liquefied Petroleum Gas (LPG) are considered a promising energy source and in many countries provide fuel cost savings. LPG coupled with DI two-stroke technologies, is expected to be clean and cost effective retrofit solution for two-stroke engines. In this research project, direct injection (DI) of Liquefied Petroleum Gas (LPG) is introduced and tested on a typical two-stroke engine. Results of in cylinder combustion pressure translated to fuel mass fraction burned, engine performance and exhaust emissions are taken and compared for various injection timings from premixed (early injection) to fully direct injection mode (late injection). Results show that DI of LPG effectively reduces exhaust hydrocarbon and can substantially improve the fuel economy of two-stroke engines.

152 スモーク法による小型2ストローク機関におけるシリンダ内流れの可視化に関する研究(エンジンシステム/動力エネルギシステム,一般講演)

152 スモーク法による小型2ストローク機関におけるシリンダ内流れの可視化に関する研究(エンジンシステム/動力エネルギシステム,一般講演)

151 小型2st内燃機関のAl-Si合金製シリンダとリング間のトライボロジーに関する研究(エンジンシステム/動力エネルギシステム,一般講演)

151 小型2st内燃機関のAl-Si合金製シリンダとリング間のトライボロジーに関する研究(エンジンシステム/動力エネルギシステム,一般講演)