Test bench development and implementation for experimental determination of mechanical losses in single cylinder internal combustion engines

As mechanical efficiency has great relevance in the alternative engine performance, the authors research in the development of testing facilities to characterize the sources of engine mechanical losses. The present paper deals with the realization of a hardware platform to conduct experimental studies in small combustion engines to experimentally characterize the mechanical losses of a single-cylinder internal combustion engine by means of the indicated diagram and motoring methods. The system was completed by means of an electrical motor-generator coupled to a single-cylinder air-cooled spark ignition engine, a self-developed electronic hardware control, and a PC-based instrumentation and data acquisition system. Specifications of load-motoring-starting system, including the description of the proprietary electronic load regulation system, are detailed. Also, the instrumentation system of in-cylinder and intake pressures; Temperatures of intake air, exhaust gases, lubricant oil, and engine block; effective torque and crankshaft position are described, including the signal acquisition system. The methodologies for indicated diagram and motoring method are described, mentioning the required measurements to apply each method and the engine load-temperature considerations when an engine is tested in fired or motored conditions. The platform was used to study the mechanical losses of the engine under motored and fired conditions under a wide range of rotational speeds and throttle openings, allowing to draw conclusions about the operating features of the developed test bench in itself, and also about the mechanical losses of the engine tested. Initially, samples of cylinder pressure, torque, intake pressure as function of crank angle and indicate diagram were obtained, showing similar waveforms present in related literature. Then, variations of the aforementioned temperatures against rotation speed and throttle opening and results for the mechanical losses determined by indicated diagram and motoring methods are shown. Finally, two empirical correlations are proposed to estimate the mechanical losses. In the future the hardware platform will be utilized to investigate in-cylinder engine parameters, detailed thermal and mechanical engine performanc

THERMAL CHARACTERIZATION OF A GASOLINE TURBOCHARGED DIRECT INJECTION (GTDI) ENGINE UTILIZING LEAN OPERATION AND EXHAUST GAS RECIRCULATION (EGR)

The push for improved fuel economy and reduced emissions has led to great achievements in engine performance and control. These achievements have increased the efficiency and power density of gasoline engines dramatically in the last two decades. With the added power density, thermal management of the engine has become increasingly important. Therefore it is critical to have accurate temperature and heat transfer models as well as data to validate them. With the recent adoption of the 2025 Corporate Average Fuel Economy(CAFE) standard, there has been a push to improve the thermal efficiency of internal combustion engines even further. Lean and dilute combustion regimes along with waste heat recovery systems are being explored as options for improving efficiency. In order to understand how these technologies will impact engine performance and each other, this research sought to analyze the engine from both a 1st law energy balance perspective, as well as from a 2nd law exergy analysis. This research also provided insights into the effects of various parameters on in-cylinder temperatures and heat transfer as well as provides data for validation of other models. It was found that the engine load was the dominant factor for the energy distribution, with higher loads resulting in lower coolant heat transfer and higher brake work and exhaust energy. From an exergy perspective, the exhaust system provided the best waste heat recovery potential due to its significantly higher temperatures compared to the cooling circuit. EGR and lean combustion both resulted in lower combustion chamber and exhaust temperatures; however, in most cases the increased flow rates resulted in a net increase in the energy in the exhaust. The exhaust exergy, on the other hand, was either increased or decreased depending on the location in the exhaust system and the other operating conditions. The effects of dilution from lean operation and EGR were compared using a dilution ratio, and the results showed that lean operation resulted in a larger increase in efficiency than the same amount of dilution with EGR. Finally, a method for identifying fuel spray impingement from piston surface temperature measurements was found. Note: The material contained in this section is planned for submission as part of a journal article and/or conference paper in the future

The Scaling of Performance and Losses in Miniature Internal Combustion Engines

Miniature glow ignition internal combustion (IC) piston engines are an off-the-shelf technology that could dramatically increase the endurance of miniature electric power supplies and the range and endurance of small unmanned air vehicles provided their overall thermodynamic efficiencies can be increased to 15% or better. This thesis presents the first comprehensive analysis of small (reliable measurements of engine performance and losses in these small engines. Methodologies are also developed for measuring volumetric, heat transfer, exhaust, mechanical, and combustion losses. These instruments and techniques are used to investigate the performance of seven single-cylinder, two-stroke, glow fueled engines ranging in size from 15 to 450 g (0.16 to 7.5 cm3 displacement). Scaling rules for power output, overall efficiency, and normalized power are developed from the data. These will be useful to developers of micro-air vehicles and miniature power systems. The data show that the minimum length scale of a thermodynamically viable piston engine based on present technology is approximately 3 mm. Incomplete combustion is the most important challenge as it accounts for 60-70% of total energy losses. Combustion losses are followed in order of importance by heat transfer, sensible enthalpy, and friction. A net heat release analysis based on in-cylinder pressure measurements suggest that a two-stage combustion process occurs at low engine speeds and equivalence ratios close to 1. Different theories based on burning mode and reaction kinetics are proposed to explain the observed results. High speed imaging of the combustion chamber suggests that a turbulent premixed flame with its origin in the vicinity of the glow plug is the primary driver of combustion. Placing miniature IC engines on a turbulent combustion regime diagram shows that they operate in the 'flamelet in eddy' regime whereas conventional-scale engines operate mostly in the 'wrinkled laminar flame sheet' regime. Taken together, the results show that the combustion process is the key obstacle to realizing the potential of small IC engines. Overcoming this obstacle will require new diagnostic techniques, measurements, combustion models, and high temperature materials

Impact of Discharge Duration on Lean Combustion in Spark Ignition Engines

Fuel-lean combustion in spark ignition engines is a promising strategy to improve engine efficiency. However, a fuel lean cylinder charge tends to lower the burning velocity because of the lowered chemical reactivity of the mixture, unless the flame propagation is accelerated by introducing an intensified flow field in the combustion chamber. Nevertheless, the literature reveals that the lean burn strategy with intensified flow fields can impose severe challenges on the ignition and flame development processes both in present and upcoming production engines. To address these issues and to better secure the flame kernel at the initial stage of combustion, various ignition strategies have been proposed with the aim of developing higher discharge current and longer discharge duration in the ignition processes, compared to those encountered with conventional spark ignition techniques. Moreover, while both current amplitude and duration of the plasma channel are fundamental to the flame kernel formation and development, their roles have not been fully clarified, let alone adequately quantified, in respect to the extensive variations in pressure, temperature, flow status, and mixture strength. Consequently, in this study, the impacts of discharge current amplitude and duration on the flame kernel initiation were investigated empirically using a constant volume combustion chamber and a single-cylinder research engine platform. The constant volume combustion chamber system was constructed so that a gas mixture with independently controlled pressure, composition, and flow intensity could be supplied. High-speed imaging was used to enable spatial and temporal characterizations of the flame kernel initiation process. Turbulence was generated inside the combustion chamber by a jet flow setup. A field programmable gate array (FPGA) controller was used to synchronize the controls of the sparking events, jet flow, and high-speed imaging. To achieve independent control of the discharge current amplitude and duration, the discharge current profile was modulated to form a quasi-rectangular shape by using a variety of hardware configurations and event controls. Ignition studies with various discharge current amplitudes and durations were conducted under both quiescent and flow conditions. Combustion test results showed that both discharge current amplitude and discharge duration had minimal impact on the ignition process under quiescent condition. However, under flow conditions, a longer discharge duration contributed to tailing flame kernels near the spark gap, and a higher discharge current amplitude contributed to larger flame kernels. Based on the experimental results and analysis, a correlation between the discharge current profiles and the flame kernel development was established with ultra-lean mixtures under intensified flow conditions. Additionally, the operational principles of the single-coil repetitive discharge and dual-coil offset discharge strategies were explored and explained. The necessary control algorithms for the repetitive and offset discharge strategies were established by analyzing the empirically acquired electrical waveforms of the discharge events. Finally, a preliminary investigation of the impact of discharge duration on the ignition stability was conducted using a single-cylinder research engine fitted with precise coolant conditioning, flexible air and fuel management, and comprehensive measurement and data acquisition. The experimental results indicated that a longer discharge duration contributed to improved combustion stability. However, ignition delay and combustion duration were unaffected by the prolonged discharge duration

Internal Combustion Engines

This book on internal combustion engines brings out few chapters on the research activities through the wide range of current engine issues. The first section groups combustion-related papers including all research areas from fuel delivery to exhaust emission phenomena. The second one deals with various problems on engine design, modeling, manufacturing, control and testing. Such structure should improve legibility of the book and helps to integrate all singular chapters as a logical whole

Measuring Scaling Effects in Small Two-Stroke Internal Combustion Engines

As internal combustion (IC) engines decrease in displacement, their cylinder surface area to swept volume ratio increases. Examining power output of IC engines with respect to cylinder surface area to swept volume ratio shows that there is a dramatic change in power scaling trends at approximately 1.5 cm-1. At this size, thermal quenching and friction losses are expected to dominate , so power production and efficiency characteristics suffer. Furthermore, small IC engines (100cc displacement) have limited technical performance data compared to IC engines in larger size classes. Therefore, it is critical to establish accurate performance figures for a family of geometrically similar engines in the size class of approximately 1.5 cm-1 in order to better predict the phenomena that contribute to lower efficiencies in small ICEs. A series of three two stroke, single cylinder, spark ignited, air cooled, and carbureted IC engines were tested in this study. They had a displacement of 28cc, 55cc and 85cc corresponding to cylinder surface area to swept volume ratios of 1.81 cm-1, 1.46 cm-1, and 1.28 cm-1 respectively. The engines share design features like compression ratio, gas exchange port design, and scavenging metho

Automotive Stirling engine: Mod 2 design report

The design of an automotive Stirling engine that achieves the superior fuel economy potential of the Stirling cycle is described. As the culmination of a 9-yr development program, this engine, designated the Mod 2, also nullifies arguments that Stirling engines are heavy, expensive, unreliable, demonstrating poor performance. Installed in a General Motors Chevrolet Celebrity car, this engine has a predicted combined fuel economy on unleaded gasoline of 17.5 km/l (41 mpg)- a value 50% above the current vehicle fleet average. The Mod 2 Stirling engine is a four-cylinder V-drive design with a single crankshaft. The engine is also equipped with all the controls and auxiliaries necessary for automotive operation

In-cylinder pressure resonance analysis for trapped mass estimation in automotive engines

This thesis presents a new application for in-cylinder pressure sensors in internal combustion engines. The new method takes profit of the high-frequency content of the in-cylinder pressure signal to determine the speed of sound evolution during the expansion stroke and combines this estimation with the low-frequency content of the pressure signal and a volume estimation to obtain a measurement of the trapped mass. The new method is based on the studies of the resonance phenomenon in pent-roof combustion chambers and proposes three calibration procedures to determine the resonant frequency evolution when bowl-in-piston geometries are considered. The Fourier transform has been modified in order to include harmonics with frequency variations, which allows a rapid identification of the resonant modes with no need of time-frequency analysis, e.g. STFT or WD. The main limitation of the method resides in the resonance excitation, which may be insufficient in low-load conditions, such as idle. An observer is presented to overcome that problem. The observer takes into account the dynamics of the sensors, the dynamics at the intake manifold, and combines current flow sensors with intermittent measurements, such as the trapped mass obtained by the resonance method, to provide the system with accurate and robust measurements of the trapped mass, the EGR, and the composition at the exhaust. The trapped mass obtained by the resonance method has been compared with auxiliary methods in various experimental facilities: in a SI engine, where no EGR exist, the differences founded were below 1%, in a conventional CI light-duty engine the average of the differences over 808 operating conditions accounted for a 2.64 %, in a research heavy-duty RCCI engine, with EGR, port fuel gasoline, and direct diesel injections, the average difference was 2.17 %, and in a research two-strokes single cylinder engine, where significant short-circuit and residual gases exist, the differences founded were 4.36 %. In all the studied cases the differences founded with the reference estimation can be attributed to the auxiliary method employed and its expected error. In order to demonstrate the potential of the resonance method four applications for control and diagnosis of internal combustion engines have been proposed: the estimation of residuals in engines with NVO, the prediction of knock in SI engines, the estimation of the exhaust gases temperature, and a NOx model for CI engines. In the four applications the method was compared with current methodologies and with additional sensors, demonstrating the improvement in accuracy and a cycle-to-cycle resolution.Esta tesis presenta una nueva aplicación para los sensores de presión en cámara. El nuevo método utiliza el contenido de alta frecuencia de la señal de presión en cámara para estimar la evolución de la velocidad del sonido durante la expansión de los gases de escape y combina esta estimación con el contenido de baja frecuencia de la presión en cámara y el volumen instantáneo de la cámara para obtener una medida de la masa atrapada. El nuevo método está basado en los estudios de la resonancia en cámaras de combustión cilíndricas y propone tres procedimientos de calibración para estimar la evolución de la frecuencia de resonancia en cámaras de combustión con bowl. La transformada de Fourier ha sido modificada para considerar harmónicos con frecuencias que varían en el tiempo, lo que permite una rápida identificación de los modos de resonancia sin necesidad de utilizar un análisis en tiempo frecuencia, como por ejemplo STFT o WD. La principal limitación del método es la necesidad de excitación suficiente de la resonancia, que puede impedir su uso en condiciones de baja carga como el ralentí. Para solventar este problema se ha diseñado un observador. El observador incluye las dinámicas de los sensores, las dinámicas del colector de admisión, y combina los sensores actuales de flujo con medidas intermitentes (como la medida ofrecida por el nuevo método de la resonancia) para obtener medidas de la masa atrapada, del EGR y de la composición en el escape precisas y robustas. La medida de la masa atrapada obtenida por el método de la resonancia ha sido comparado con métodos auxiliares en diferentes instalaciones experimentales: en un motor SI, sin EGR, las diferencias con los sensores eran menores del 1%, en un motor convencional CI la media de las diferencias sobre 808 puntos de operación distintos ha sido de 2.64 %, en un motor de investigación con EGR, con inyección gasolina en el colector e inyección directa de diesel, las diferencias fueron de 2.17 %, y en un motor de investigación de dos tiempos, donde existían grandes cantidades de corto-circuito y gases residuales, las diferencias fueron de 4.36 %. En todos los casos estudiados las diferencias encontradas pueden ser atribuidas a los errores que caracterizan los métodos auxiliares utilizados para obtener la medida de referencia. Finalmente, para demostrar el potencial del método se han desarrollado cuatro aplicaciones para control y diagnóstico de motores de combustión interna alternativos: la estimación de gases residuales en motores con NVO, la predicción de knock en motores SI, la estimación de la temperatura de los gases de escape, y un modelo de NOx para motores CI. En las cuatro aplicaciones el método ha sido comparado con los sistemas de medidas actuales y con sensores adicionales, demostrando mejoras importantes en la precisión de la medida y una resolución de un solo ciclo.Aquesta tesi presenta una nova aplicació per als sensors de pressió en cambra. El nou mètode utilitza el contingut d'alta freqüència del senyal de pressió en cambra per estimar l'evolució de la velocitat del so durant l'expansió dels gasos d'eixida i combina aquesta estimació amb el contingut de baixa freqüència de la pressió en cambra i el volum instantani de la cambra per obtenir una mesura de la massa atrapada. El nou mètode està desenvolupat dels estudis de la ressonància en cambres de combustió cilíndriques i proposa tres procediments de calibratge per estimar l'evolució de la freqüència de ressonància en cambres de combustió amb bowl. La transformada de Fourier ha sigut modificada per considerar harmònics amb freqüències que varien en el temps, el que permet una ràpida identificació dels modes de ressonància sense necessitat d'utilitzar una anàlisi en temps-freqüència, com per exemple la STFT o la WD. La principal limitació del mètode és la necessitat d'excitació suficient de la ressonància, que pot impedir el seu ús en condicions de baixa càrrega, com al ralentí. Per solucionar aquest problema s'ha desenvolupat un observador. L'observador inclou les dinàmiques dels sensors, les dinàmiques del col·lector d'admissió, i combina els sensors actuals de flux amb mesures intermitents (com l'obtinguda pel nou mètode de la ressonància) per obtenir mesures de la massa atrapada, del EGR i de la composició d'eixida precises i robustes. La mesura de la massa atrapada obtinguda pel mètode de la ressonància ha sigut comparada en mètodes auxiliars en diferents instal·lacions experimentals: a un motor SI, sense EGR, les diferencies amb els sensors estaven per davall de l'1 %, a un motor convencional CI la mitja de les diferències sobre 808 punts d'operació diferents ha sigut de 2.64 %, a un motor d'investigació, en EGR, en injecció gasolina en el col·lector i injecció directa de dièsel, les diferències van ser de 2.17 %, i a un motor d'investigació de dos temps, on existien grans quantitats de curtcircuit i residuals, les diferencies foren de 4.36 %. En tots els casos estudiats les diferències trobades poden ser atribuïdes als errors que caracteritzen els mètodes auxiliars utilitzats per obtenir la mesura de referència. Finalment, per demostrar el potencial del mètode s'han desenvolupat quatre aplicacions per al control i diagnòstic de motors de combustió interna alternatius: l'estimació de gasos residuals en motors amb NVO, la predicció de knock en motors SI, l'estimació de la temperatura dels gasos d'eixida, i un model de NOx per a motors CI. En les quatre aplicacions el mètode ha sigut comparat amb els sistemes de mesures actuals i amb sensors addicionals, demostrant millores importants en la precisió de la mesura i una resolució de solament un cicle.Bares Moreno, P. (2017). In-cylinder pressure resonance analysis for trapped mass estimation in automotive engines [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/9042

Specifications for modelling fuel cell and combustion-based residential cogeneration device within whole-building simulation programs

This document contains the specifications for a series of residential cogeneration device models developed within IEA/ECBCS Annex 42. The devices covered are: solid oxide and polymer exchange membrane fuel cells (SOFC and PEM), and internal combustion and Stirling engine units (ICE and SE). These models have been developed for use within whole-building simulation programs and one or more of the models described herein have been integrated into the following simulation packages: ESP-r, EnergyPlus, TRNSYS and IDA-ICE. The models have been designed to predict the energy performance of cogeneration devices when integrated into a residential building (dwelling). The models account for thermal performance (dynamic thermal performance in the case of the combustion engine models), electrochemical and combustion reactions where appropriate, along with electrical power output. All of the devices are modelled at levels of detail appropriate for whole-building simulation tools