Povećanje performansi dvotaktnog Otto motora optimiranjem detonacijskog izgaranja

All high-efficiency engines are inclined to destruction tendencies resulting from detonation combustion. Most often the producers of engines solve this problem with limitation of maximum output performance but, in this, there is an efficiency decrease of fuel utilization. However, detonation combustion can also be useful because if it is kept to a certain level, then detonation combustion helps considerably in an additional increase of output performance. This article defines the termination expressed in a number of detonation units per overridden distance of track carried out by a single-track vehicle. Just for this limit, there is a detonation combustion beneficial to increase an output performance and not cause destruction in the engineering parts of an engine. The limit gives an idea about the influence of individual factors on detonation combustion as well as the influence on this combustion in obtaining maximum values and behaviours of engine output performance and torque with dependence on engine speed.Svi visoko učinski motori naginju detonacijskom načinu izgaranja. Mnogi proizvođači motora rješavaju taj problem ograničavanjem maksiomalnih izlaznih performansi motora, a što ima za posljedicu smanjenje stupnja iskoristivosti tog motora. No ipak detonacijsko izgaranje može biti i od koristi, jer ako se ono podržava na stvarnoj razini, tada takav način izgaranja omogućava primjetno povećavanje izlaznih performansi motora. Ovaj članak definira ograničenje broja detonacijskih jedinica nad cjelokupnim putanjom, koje je prešlo vozilo. Upravo za to ograničenje postoji benefit detonacijskog izgaranja u smislu povećavanja izlaznih performansi, a pri čemu ne dolazi do oštećivanja bilo kojeg drigog dijela motora. To ograničenje daje ideju o utjecaju pojedinačnih faktora na detonacijsko izgaranje, kao i utjecaj ovakvog načina izgaranja na dobivanje maksimalnih vrijednosti kao i na ponašanja izlaznih performansi motora i momenta ovisno o brzini motora

Engine Output Increase of Two-stroke Combustion with Exhaust System Optimization

In principle, an exhaust system influences the maximum output and characteristic of a two-stroke combustion engine. The first part of the contribution deals with the possibility of transformation in a maximum output and a range of exploitable speed values by means of the change of exhaust manifold length in exhaust pipe section. This knowledge covers an output curve variability of an engine operating speed range. The second part of this contribution deals with the combustion product\u27s temperature influence in an exhaust system for a maximum engine output and a range of exploitable speed. By increasing the combustion product\u27s temperature in an exhaust system, the maximum engine output is reduced overall. There is the transfer of engine output to higher engine speed because the exhaust manifold length is short theoretically. That is why it is necessary to provide the optimum value of combustion products temperature in an exhaust system and so achieve maximum values of outgoing parameters

A similarity model of specific heat loss determined by dimensional analysis

This article describes an innovative method for the determination of heat flow (specific heat loss; linear heat flow density) from a one-metre length of a twin pipe directly-buried heat network. Such heat losses are currently described by applying analytical procedures based on the heat transfer theory. It is rather complicated to accurately express the heat loss using such procedures, due to the necessity to determine the individual values of thermal resistance. A simpler method to express heat loss is the balance method, as it requires measuring a temperature gradient ∆t between the starting point of the heat network and the end point of the heat collection. A suitable measuring device must provide high-accuracy measurements of the temperature. In the case of very well insulated distribution pipelines and short pipes, the temperature measurements must be accurate to the hundredths of a degree Celsius. It is impossible to install such devices as fixed equipment on every heat distribution network, due to such networks measuring many kilometres and the cost of the appropriate measuring technology. For the aforesaid reasons, the authors created a mathematical model for specific heat losses based on dimensional analysis. This method facilitates the identification of dimensionless criteria based on the relevant dimensional quantities. Functional correlations between the identified criteria may be identified on the basis of the results of physical or numerical experiments. In this study, a database of the results obtained from physical experiments conducted on two heat networks was used. The output of the similarity model was a function describing the heat flow from a one-meter pipe length that was applicable to various alternatives in relation to the geometrical, physical and boundary conditions. The standard deviation of a difference in the heat losses identified by applying the balance method and using the proposed criterial equation for a twin pipe directly-buried pre-insulated heat network was 0.515 W·m−1.Web of Science1314art. no. 805

Advanced System Determined for Utilisation of Sustainable Biofuels in High-Performance Sport Applications

It is of current importance to reach carbon neutrality in various transport sectors as soon as possible, with regard to the fact that transport, characterized by the utilization of piston combustion engines, is one of the main polluters in urban agglomerations. Piston combustion engine pollution also significantly influences the quality of the living environment and human health. The application of biofuels containing bioethanol or biodiesel essentially contributes to the reduction of air pollution caused by exhaust gases, also taking into consideration the renewability of these fuels. Therefore, the modification of spark ignited engines is necessary for the correct operation of ethanol combustion and to remove risks during operation and combustion, mainly the possibility of detonation combustion. To date, there has been a gradual development of engines intended for the combustion of the fuel mixture gasoline–bioethanol, mainly the fuel E85. This fuel mixture contains 85% ethanol and 15% gasoline. This paper is focused on construction modifications of a specific combustion engine, which operates with a two-stroke working cycle, which is predominantly intended for installation in category L motor-sport vehicles and kart race vehicles. A new construction solution specifically for this engine was developed and consequently patented. The results obtained while testing this engine in real racing conditions confirmed the correctness and purposefulness of the proposed engine concept

Analýza kritických miest v konštrukcií piesta s cieľom eliminácie rizík pri aplikácii HCCI technológie

This work was supported by the Slovak Research and Development Agency under the contract No. APVV-16-0259.Application of the HCCI technology was till now limited due to several principal problems, such as high compression ratios and excessive heat release. Both these factors are influencing local strength of the individual constructional parts concerning the piston combustion engine, whereby the most critical constructional part is the engine piston. A casted Vertex piston was analysed with the aim to find the areas where local stress and local strength are ciritical for the safety. The casting affects the properties of the used material which was a transeutectic silumin (aluminum-base casting alloy containing about 12 at % of silicon). The critical areas are the places in the structure where the relation "local stress/local strength" reaches the maximum value. Local strength of the investigated material was estimated using a material modell based on the relation between the strength and the mean distance between dendrite arms (secondary dendrite arms spacing = SDAS) in the casted microstructure. The differencies in the strength value can reach in the casted bulk mictrostructure, due to local heterogeneities, up to 15%. Using the FEM analysis, Fig. 1, the stress distribution in the piston was modelled and, on the other hand, based on SDAS measuring in the casted microstructures extracted from critical areas, the local strength values were calculated for various microstructures. Based on the relation "local stress/local strength" calculated for various localities the critical places were located in the piston, Fig. 2

Vehicle emissions and environmental risks in urban destinations

Tato práca bola podporovaná Agentúrou na podporu výskumu a vývoja na základe Zmluvy č. APVV-16-0259.Tento príspevok stručne popisuje aktuálne emisné problémy vozidiel a environmentálne riziká, ktoré predstavujú najmä pre mestské destinácie. Do vývoja nových motorov a protiemisných opatrení sa musia investovať veľké čiastky, ktoré sa vynakladajú často s neistým výsledkom. Využívajú sa rôzne techniké riešenia, ktoré tvorbu oxidov dusíka obmedzujú alebo NOx likvidujú. Riešením by mohla byť technológia HCCI. Predchádzajúce a súčasné výskumné práce vo svete naznačili, že motor pracujúci v režime HCCI ponúka výraznú úsporu paliva. Okrem toho homogénne miešanie paliva sa vzduchom vedie k čistejším emisiám a úroveň emisií oxidov dusíka je takmer zanedbateľná

INFLUENCE ANALYSIS OF DETONATIONS RELATED TO OUTPUT CHARACTERISTICS AND TO DAMAGE LEVEL OF ENGINE PARTS IN ORDER TO ELIMINATE POTENTIAL RISKS AND ENSURE RELIABILITY OF THE HCCI TECHNOLOGY

The engine output characteristic offers very important information during the real application of the HCCI technology. This kind of combustion process significantly influences the wearing degree of the main engine components or even the engine damage. The principle of the HCCI combustion is basically beneficial, however, it can also be destructive. Described in this article are measurements of the engine output characteristics in the case of an experimental piston combustion engine. These measurements were performed by means of a data recording system, whereby the detonation combustion was evaluated using a quantitative method. The real values of atmospheric conditions and fuel mixture composition were added to the measured values. The resulting values were visually compared with a degree of the engine piston damage caused by the detonations. The final result is a limit value, which represents a maximal number of the detonation units that are permissible in order to ensure reliable operation of the HCCI engine

INFLUENCE OF VARIOUS HOMOGENISATION SYSTEM CONFIGURATIONS ON OUTPUT PARAMETERS OF AN EXPERIMENTAL ENGINE

This article analyses the influence of various configurations concerning the homogenisation system on the output parameters of an experimental engine. The results presented in this article were obtained using experimental dynamometric measurement. A modular approach to the individual measurements consists of a sequential formation of the homogenisation system configurations. The experimentally obtained results are matches with the analytical relations, which are described in the related literature. These results can be presented for a wide spectrum of high-powerful engines because the homogenisation system does not depend on the construction and design arrangement of the engine itself. The analysed system was successfully applied in the motorcycles and it is a subject of the patent application