Ideal Otto Cycle Research Articles

Energy valorization strategies of fallen leaves and woody biomass in a based downdraft gasification-engine power plant

Herein the effect of ash-rich biomass (fallen-leaves, FL) mixed with woody biomass (WB) on the thermodynamic performance of a bioenergy power plant based on a downdraft gasifier coupled to an engine-generator (<20 kW) is analyzed. The WB mass fraction in the mixtures ranged from 0% to 100% which led to the making of five samples (FL100, FL75-WB25, FL50-WB50, FL25-WB75, and WB100). The biopower plant was modelled using the Aspen Plus and Engineering Equation Solver (EES) software under the thermochemical and Ideal Otto cycle approaches. The gasification model validation with experimental data from the literature reached a 6.6% relative error. The implemented model was used to assess garden-waste energy valorization strategies by contrasting their chemical characterization (ash fusibility temperatures) with the power plant performance. The energy recovery of FL with WB showed a positive effect on the specific fuel consumption and the power generated by the biopower plant, which were enhanced by 7% and 6%, respectively, with the FL25-WB75 mixture when compared to FL100. Nevertheless, cold gas and overall plant efficiencies decreased by ∼18% on average due to the solid fuel higher heating value as the WB fraction increased. This behavior was found when keeping the reactor temperature below ∼1000 °C to avoid ash deposition issues, such as fouling and slagging.

Internal geometric friction in a Kitaev-chain heat engine

We investigate a heat engine with a finite-length Kitaev chain in an ideal Otto cycle. It is found that the critical point of the topological phase transition coincides with the maxima of the efficiency and work output of the total Otto engine. Finite-size effects are taken into account using the method of Hill's nanothermodynamics, as well as using the method of temperature-dependent energy levels. We identify the bulk and boundary thermal cycles of the Kitaev chain engine and find that they are non-ideal Otto cycles. The physics of deviation from ideal Otto cycle is identified as a finite size effect, which we dub as "internal geometric friction", leading to heat transfer from the bulk to the boundary during adiabatic transformation of the whole system. Besides, we determine the regimes allowing for independently running an ideal Otto refrigerator at the boundary and an ideal Otto engines in the bulk and in the whole system. Furthermore, we show that the first-order phase transition in the boundary and the second-order phase transition in the bulk can be identified through their respective contributions to the engine work output.

Numerical comparison of combustion characteristics and cost between hydrogen, oxygen and their combinations addition on natural gas fueled HCCI engine

Hydrogen, oxygen, and their combinations as effective species in the production of radical OH, which plays an effective role in the HCCI combustion enhancement, are considered to study their effect on combustion characteristics and resolving the challenges facing natural gas HCCI engines numerically. There are five items were considered for adding oxygen, hydrogen and their compounds, including 1%, 2%,3%, 4% and 5% of the fuel mixture for hydrogen, 10%, 20%, 30%, 40% and 50% for the extra oxygen in oxidizer and add up half of each respectively, including 0.5% H2 + 5%O2, 1% H2 + 10%O2, 1.5% H2 + 15%O2, 2% H2 + 20%O2, and 2.5% H2 + 25%O2. Adding hydrogen to some extent improves the engine efficiency, lowers combustion duration, and brings the engine cycle closer to the ideal Otto cycle and reduces CO and UHC emissions, but it can only increase engine operating range by as much as 4.2% at low load, increases NO emission, and increases the combustion noise. Hydrogen addition results in faster methane combustion, shortens the fuel combustion duration and increases the OH radical concentration. Up to 30%, added oxygen can extend the engine working range up to 48% at low loads, making the engine run smoother and shortening the combustion duration, although IMEP and efficiency decrease, CO and UHC emissions increase. By using hydrogen and oxygen compounds obtained their both benefits simultaneously, the engine operating range expands by 40.19% at low loads, the emissions would be less than the Euro 6 standard limitation and the maximum difference in efficiency is only 2.38% less than hydrogen addition. By adding these additives, ignition delay decreases and SOC advances. Using hydrogen and oxygen to improve engine performance at low loads is an appropriate and affordable solution, which does not cost much.

Energy efficiency of automotive gasoline engine: current approaches

Introduction. To meet the promising requirements fuel consumption and CO 2 emissions of passenger cars and commercial vehicles of 2025-2030 further improvement of the design and workflowof a gasoline internal combustion engine (ICE) is required in the full range of the working map, especially at high loads. The purpose of the study was to review and analyze ways to improve the indicator efficiency of a gasoline ICE and approaches aimed at increasing efficiency by reducing heat losses. Methodology and research methods . The review of barriers to increasing the indicator efficiency of a gasoline ICE was based on the analysis of the ideal and real Otto cycle and the results of experimental and calculated foreign and domestic studies of recent years aimed at increasing fuel efficiency by reducing heat losses. Scientific novelty and results . It was shown that effective new approaches to reduce the heat losses of the ICE of the future were: organization of combustion of a stoichiometric mixture diluted with a large amount of cooled recirculated exhaust gases (up to 25-35%) at high loads; increasing the ratio of the piston stroke to the cylinder diameter S/D to a value of the order of 1.5; the use of thin thermal barrier coatings that provide a “temperature swing” of the combustion chamber surface. Combined with proven modern technologies (direct fuel injection, variable valve drive, etc.), they can significantly increase the optimal geometric compression ratio, significantly reduce heat loss to the walls of the combustion chamber and the tendency of the ICE to detonate, and provide an increase in the indicator efficiency up to 49-53%. The practical significance lies in the possibility of using the results of the work when choosing a scheme and design solutions for a promising gasoline ICE with reduced fuel consumption and CO 2 emissions.

Effects of molar expansion ratio of fuels on engine efficiency

Fuel properties have a strong impact on the efficiency of internal combustion engines. Contrary to other physical and thermochemical fuel properties, the molar expansion ratio is normally ignored. Molar expansion ratio is the ratio of number of moles of the products to the reactants. In this work, the impact of the fuel’s molar expansion ratio on engine efficiency is investigated. Findings are based on simulations of a spark ignition engine using different fuels (standard fuels and user-defined fuels) and different dilution ratios. Simulations without heat transfer and friction were performed first. The combustion then takes place at top dead center with a very short combustion duration to approach the ideal Otto cycle. The heat transfer and friction were then added step by step. From this analysis, it could be concluded that the heat loss and friction work decrease as molar expansion ratio increases. The gross indicated and brake thermal efficiencies thus increase. User-defined fuels with different molar expansion ratio, but the same physical and thermochemical properties were then employed. The simulated results showed that the brake thermal efficiency increases by around 1.15% with an increase in molar expansion ratio of 0.02 compared to a fuel with a molar expansion ratio of unity. The simulation was also done with air and exhaust gas recirculation dilution.

Modeling novel methodologies for unmanned aerial systems – Applications to the UAS-S4 Ehecatl and the UAS-S45 Bálaam

The rising demand for Unmanned Aerial Systems (UASs) to perform tasks in hostile environments has emphasized the need for their simulation models for the preliminary evaluations of their missions. The efficiency of the UAS model is directly related to its capacity to estimate its flight dynamics with minimum computational resources. The literature describes several techniques to estimate accurate aircraft flight dynamics. Most of them are based on system identification. This paper presents an alternative methodology to obtain complete model of the S4 and S45 unmanned aerial systems. The UAS-S4 and the UAS-S45 models were divided into four sub-models, each corresponding to a specific discipline: aerodynamics, propulsion, mass and inertia, and actuator. The “aerodynamic” sub-model was built using the Fderivatives in-house code, which is an improvement of the classical DATCOM procedure. The “propulsion” sub-model was obtained by coupling a two-stroke engine model based on the ideal Otto cycle and a Blade Element Theory (BET) analysis of the propeller. The “mass and the inertia” sub-model was designed utilizing the Raymer and DATCOM methodologies. A sub-model of an actuator using servomotor characteristics was employed to complete the model. The total model was then checked by validation of each sub-model with numerical and experimental data. The results indicate that the obtained model was accurate and could be used to design a flight simulator.

Otto refrigerator based on a superconducting qubit: Classical and quantum performance

We analyse a quantum Otto refrigerator based on a superconducting qubit coupled to two LC-resonators each including a resistor acting as a reservoir. We find various operation regimes: nearly adiabatic (low driving frequency), ideal Otto cycle (intermediate frequency), and non-adiabatic coherent regime (high frequency). In the nearly adiabatic regime, the cooling power is quadratic in frequency, and we find substantially enhanced coefficient of performance $\epsilon$, as compared to that of an ideal Otto cycle. Quantum coherent effects lead invariably to decrease in both cooling power and $\epsilon$ as compared to purely classical dynamics. In the non-adiabatic regime we observe strong coherent oscillations of the cooling power as a function of frequency. We investigate various driving waveforms: compared to the standard sinusoidal drive, truncated trapezoidal drive with optimized rise and dwell times yields higher cooling power and efficiency.

Modified Compression Ratio Effect on Brake Power of Single Piston Gasoline Engine Utilizing Producer Gas

An objective of this research is to test the brake power of Honda Model GX-120-four strokes-spark ignited engine. The producer gas was made from dry wood by the gasification process. The producer gas was used as a fuel for the engine. To study the effect of compression ratio and percentage of opened air inlet valve on break power, the compression ratio of 7.5:1 and 9.3:1 and percentage of opened air inlet valve of 30% and 75% were used. It was found that the brake power of compression ratio at 9.3:1 with 75% of opened air inlet valve was 1,443.6 Watts at 3,800rpm showed the highest break engine power because the high compression ratio was high, and the brake power was also high as the basic theory of an ideal Otto cycle.

Otto engine beyond its standard quantum limit.

We propose a quantum Otto cycle based on the properties of a two-level system in a realistic out-of-thermal-equilibrium electromagnetic field acting as its sole reservoir. This steady configuration is produced without the need of active control over the state of the environment, which is a noncoherent thermal radiation, sustained only by external heat supplied to macroscopic objects. Remarkably, even for nonideal finite-time transformations, it largely over-performs the standard ideal Otto cycle and asymptotically achieves unit efficiency at finite power.

Fundamental Explorations of Spring-Varied, Free Piston Linear Engine Devices

The conventional crank-based internal combustion engine faces many challenges to remain a viable option for electric power generation. Limitations in mechanical, thermal, and combustion efficiencies must be overcome by innovations in existing technologies and progress toward new ones. The free piston linear engine (FPLE) has the potential to meet these challenges. Friction losses are reduced by avoiding rotational motion and linkages. Instead, electrical power is generated by the oscillation of the translator through a stator. Naturally, variable compression ratio provides a unique platform to employ advanced combustion regimes. However, possibly high variations in stroke length result in unknown dead center piston positions and greater difficulties in compression control as compared to conventional engines. Without control, adverse occurrences such as misfire, stall, over-fueling, and rapid load changes pose greater complications for stable system operation. Based on previous research, it is believed that incorporating springs will advance former designs by both increasing system frequency and providing a restoring force to improve cycle-to-cycle stability. Despite growing interest in the FPLE, current literature does not address the use of springs within a dual, opposed piston design. This investigation is an extension of recent efforts in the fundamental analysis of such a device. Previous work by the authors combined the dynamics of a damped, spring mass system with in-cylinder thermodynamic expressions to produce a closed-form nondimensional model. Simulations of this model were used to describe ideal Otto cycle as the equilibrium operating point. The present work demonstrates more realistic modeling of the device in three distinct areas. In the previous model, the work term was a constant coefficient over the length of the stroke, instantaneous heat addition (representing combustion) was only seen at top dead center (TDC) positions, and the use of the Otto cycle included no mechanism for heat transfer except at dead center positions. Instead, a position based sinusoid is employed for the work coefficient causing changes to the velocity and acceleration profiles. Instantaneous heat addition prior to TDC is allowed causing the compression ratio to decrease toward stable, Otto operation, and a simple heat transfer scheme is used to permit cylinder gas heat exchange throughout the stroke resulting in deviation from Otto operation. Regardless, simulations show that natural system stability arises under the right conditions. Highest efficiencies are achieved at a high compression ratio with minimal heat transfer and near-TDC combustion.

1732 火花点火機関のノッキングに対する空燃比の影響

Effect of equivalence ratio on knocking in homogeneous spark ignition engines was investigated by using a single cylinder engine. Knocking was evaluated by an index of the degree of constant volume, which showed how close to the ideal Otto cycle the tested cycle was. Petrol but also n-butane, iso-octane and toluene were tested. The maximum tendency to knock around the stoichiometric mixture was confirmed on the condition of the same manifold pressure. However, further experimental work indicated that the maximum tendency to knock shifted from the stoichiometric mixture to the lean mixture if the charge fuel was constant.

Second-law analysis of an ideal Otto cycle

The system input and output exergy at each portion of an ideal Otto cycle, as well as the process effectiveness, are calculated for compression ratios of 3.0:9.0 and air/fuel equivalence ratios of 0.25:1.0. For comparison, the energy-based efficiencies are also calculated. It was found that both effectiveness and efficiency increase with compression ratio and with air-to-fuel ratio (but at different rates), and that the effectiveness does not vary much when the air-to-fuel ratio increases above 200%. It was also shown that exergy analysis represents the losses in the cycle, such as in the combustion and exhaust processes, much more realistically than the conventional first-law analysis and serves as a good guide for cycle improvements. Several recommendations are made in that direction.

Theoretical limits of engine economy with alternative automotive fuels

Calculations have been made of the theoretical limits of engine efficiency for various fuels. Considered were methanol, ethanol, benzene, iso-octane, ethane and methane. The ideal Otto cycle was used for the calculations, since it represents the upper limit for fast-burn adiabatic engines. At the conditions explored, small differences in thermodynamic cycle efficiency of under 2 per cent exist among the various fuels. These differences can be explained by the thermodynamic properties of the fuel/air mixtures themselves.

Optimal paths for thermodynamic systems: The ideal Otto cycle

We apply the method of optimal control theory to determine the optimal piston trajectory for successively less idealized models of the Otto cycle. The optimal path has significantly smaller losses from friction and heat leaks than the path with conventional piston motion and the same loss parameters. The resulting increases in efficiency are of the order of 10%.

Performance of Otto Engine by Extremely Rich Mixture of Methane-Oxygen

Natural gas is generally used as raw material for chemical industry as well as for fuel of internal combustion engine. Hence, the power output and the composition of exhaust gas were calculated by assuming the ideal Otto cycle, and compared its result with that obtained by modified CFR engine supplied by extremely rich mixture of Methane-Oxygen.According to the results of experiment, the exhaust gas was mainly composed of hydrogen and carbon monoxide, both necessary for synthetic gas at the maximum percentage of 61 and 42 respectively and power output up to 1.5kWhr/m3 of methane was obtained which was able to produce necessary oxygen.The power output was considerably small due to the extremely rich mixture but the engine ran smoothly in spite of pure oxygen and any abnormal combustion was not marked even in the indicater diagram by Piezo Type Indicator. The amount of formation of free carbon was negligibly small, which made the exhaust gas almost colorless. Almost no carbonaceous deposit was observed on the surface of combustion chamber after repeated intermittent runnings for a long time.If the combustion chamber of the internal combustion engine were used for chemical reactor, it was considered to be an excellent compact one having the ability of instantaneous start and stop, since the control of the reaction was simple and reliable.