Intake Air Temperature Research Articles

Analysis of Combustion Conditions for Sustainable Dual-Fuel Mixtures

The scientific contribution is focused on the analysis and optimization of combustion conditions concerning the dual-fuel mixtures. The greatest attention was paid to the temperature of intake air when a mixture of ethanol and gasoline created the applied fuel. An experimental fuel mixture was added into the intake pipe and ultra-low sulphur diesel fuel (ULSDF) was added directly into the engine cylinder using the CR (common rail) injection system. The article analysed the medium- and high-level operational engine load, whereby the engine timing parameters originally corresponded to a conventional diesel engine. The obtained results of the performed analysis showed that the temperature of intake air affected the following operational parameters: delay of ignition, pressure rise rate in the engine cylinder and the maximum level of pressure in the engine cylinder. Lower values of the intake air temperature enabled higher injection speeds for the ethanol–sustainable mixture (ESM), especially at high engine loads. An increase in the injection speed was possible due to lower charge air temperature. While there were reduced nitrogen oxide emissions, we also noted a reduction in both carbon monoxide emissions and the total amount of unburned hydrocarbon emissions.

Numerical investigation of lamella heat exchanger for engine intake charge air cooling utilizing refrigerant as coolant medium

Intercooler heat exchangers (IHE) are used to improve engine charge air temperature, which enhances engine efficiency and reduces emissions. The current study introduces a novel intercooler heat exchanger designed to improve combustion and engine performance by providing cold intake air. Lamella heat exchanger is proposed, based on space availability in existing engines, operated as an evaporator utilizing a refrigeration unit, the same used for vehicle compartment cooling. A numerical investigation is carried out for a 1.496 L naturally aspirated engine at rpm 4000, 5000, and 6000. The intake air temperature is taken as 45 °C to examine the proposed four models: model A, model B, model C & model D bearing aspect ratios of 21.6 mm, 27 mm, 36 mm & 43.2 mm, respectively. The study aims to obtain high heat transfer with minimal pressure loss. For that, the evaluation criteria for all models are heat transfer, temperature drop, number of transfer units, logarithmic mean temperature difference, and pressure drop. As a result, all models under consideration are ranked from high to low; model D, model C, model B, and model A. The maximum heat transfer of 1.55 KW and the maximum temperature drop of 24.06 °C are observed for model D at rpm of 6000 and 4000, respectively. Likewise, the maximum pressure drop is recorded for model D at all rpm ranges; still, the pressure drop for model D is less than 28 % of the reference model used in this study at 6000 rpm. The simulated results indicate that all evaluation parameters except LMTD are directly proportional to the aspect ratio of the lamella. Due to their compactness, the proposed heat exchanger designs offer more surface area per unit volume, resulting in higher thermal capacity than the other conventional intercooler heat exchangers.

Efficient and clean combustion of intelligent charge compression ignition (ICCI) engine at low load conditions

The efficient and clean combustion of compression ignition (CI) engines under low load conditions has always been a challenge. Intelligent charge compression ignition (ICCI) mode has been proved to be able to effectively control the combustion phase and heat release rate which has great potential to improve engine efficiency. In this paper, the combustion and emission characteristics of ICCI mode under low load conditions with indicated mean effective pressure (IMEP) from 2 to 6 bar were explored. Commercial diesel was selected as high-reactivity fuel, commercial gasoline with the research octane number (RON) of 95 and three low-octane gasolines with RON of 85, 80 and 75 were tested as the low-reactivity fuel. The results show that by optimizing the fuel injection strategies and gasoline ratio, the indicated thermal efficiency (ITE) at IMEP of 6 bar could reach above 50 % with commercial gasoline as low-reactivity fuel. For IMEP of 2 bar, increasing intake air temperature and reducing intake pressure improved ITE up to 46 %. By taking RON85 as low-reactivity fuel, the ITE at IMEP of 4 bar could reach 51.4 % with the intake air temperature of 50 °C. NOx and particulate emissions were maintained at low levels under ICCI mode. Based on this study, the efficient and clean combustion of ICCI mode can be reached at IMEP of 4 bar with ITE higher than 50 %.

Development of a phenomenological model for the description of RCCI combustion in a dual-fuel marine internal combustion engine

Increasingly stringent pollutant and CO2 emission standards require engine manufacturers to investigate innovative solutions. Among these techniques, low-temperature combustion (LTC) concepts have a large potential to simultaneously reduce NOx emissions and fuel consumption. A promising manner to realize LTC consists of adopting ultra-lean mixtures, where the combustion evolution is controlled by a proper spatial distribution of fuels with different chemical reactivities. In this context, depending on the proportion and stratification of the fuels, the heat release can primarily depend on chemistry progression, leading to a Reactivity Controlled Compression Ignition (RCCI) mode, or on flame propagation, locally initiated by a high reactivity fuel.In this work, the combustion characteristics of a large-bore research engine are experimentally investigated. Natural gas is supplied into the intake port, while light fuel oil (LFO) is directly injected in the cylinder. An experimental campaign is carried out including sweeps of engine load, air/fuel proportion, LFO amount, valve timing, and intake air temperature. Global engine operating parameters as well as cylinder pressure traces are recorded and analyzed.Based on the available experimental data, a phenomenological model handling both chemistries of fuels with different reactivities and flame propagation is developed and validated. The model is based on a multi-zone approach, where auto-ignition chemistry is solved by a tabulated method to preserve the computational effort. The proposed numerical approach shows the ability to simulate the experimental data with good accuracy, using a fixed tuning constant set. A dedicated correlation is built to reproduce the expected in-cylinder distribution of the directly injected liquid fuel. Global performance and combustion parameters are predicted with an average error below 5%. The model demonstrates to correctly describe the behavior of the tested engine under different operating conditions and to capture the physics behind such advanced combustion concepts.

Fuel Efficiency Improvement & Knocking Reduction System Using 2-Stroke Petrol Engine By Coolant Injection

Abstract— In internal combustion engines, the water injection, also known as an anti-detonant injection, is spraying water into the cylinder or incoming air-fuel mixture to cool the combustion chamber of the engine, allowing for greater compression ratios and eliminating the problem of engine knocking. This effectively reduces the air intake temperature in the combustion chamber. The reduction of the air intake temperature allows for higher ignition timing to be employed, which ultimately increases the power output of the engine. Depending on the engine, improvement in power and fuel efficiency can also be obtained by injecting water. Water injection may also reduce carbon monoxide emissions. The purpose of this experiment is to investigate the effect of water injection on the engine performance, exhaust gas temperature, and exhaust emission of the S.I. engine, water is injected in specific quantities with compressed air. Single cylinder, two-stroke, air-cooled, 100 cc petrol engines were used in this experiment. Obtained data will compare to calculate the performance of specific fuel consumption, which will get without a water supply to a petrol engine based on performance. The performance test is conducted to find out the fuel efficiency and is compared with conventional engine present also emission is to be carried out to find CO (carbon monoxide) emissions. Keywords— anti-detonate injection, engine knocking, fuel efficiency, water injection, two-stroke

DESIGN, FABRICATION AND EVALUATION OF LPG-FUEL INJECTION SYSTEM FOR MOTORBIKES

Liquified Petroleum Gas (LPG) fuel is currently an energy source being widely applied in many fields in Vietnam, making a significant contribution to the development of the national economy. This paper presents research results of applying LPG fuel used in motorbikes. The traditional liquid fuel system (gasoline) on a motorbike was replaced by an electronically controlled LPG fuel injection system. LPG fuel is designed to inject into the intake manifold. The injection quantity and injection timing are calculated and controlled by the electronic control unit through the calculation and analysis of the input of key parameters such as intake air pressure and temperature, throttle position, engine speed, and camshaft position. The testing results on real roads in an urban area show that the motorbike operates stably on flat and uphill roads. In addition, the cost of LPG fuelconsumption is less than that of the gasoline fuel consumption.

Effects of intake charge temperature and relative air-fuel ratio on the deterministic characteristics of cyclic combustion dynamics of a HCCI engine

Homogenous charge compression ignition (HCCI) combustion can significantly reduce automotive pollution and increase the thermal efficiency of the engine. However, combustion phasing control is a major challenge in HCCI engines due to severe cyclic combustion variations. This study investigates the cyclic combustion dynamics of the HCCI engine using nonlinear dynamic methods such as return maps, recurrence plots (RPs), and recurrence quantitative analysis (RQA). Combustion stability and cyclic variations of HCCI combustion parameters were investigated on a modified four-stroke diesel engine. The experiments were conducted by varying relative air-fuel ratios ([Formula: see text]) and intake air temperatures ([Formula: see text]) at two engine speeds. In-cylinder pressure data of 2000 consecutive engine combustion cycles is logged for each test condition. In this study, deterministic characteristics of combustion phasing (CA50) and crank angle position of maximum cylinder pressure ([Formula: see text]) are investigated and compared by employing nonlinear dynamical methods. Return maps revealed that [Formula: see text] is having distinct and more frequently observed deterministic characteristics in comparison to CA50. Patterns in RPs showed a more persistent and sudden change in the combustion dynamics at higher engine speeds. Recurrence plot-based analysis found the existence of deterministic features in the combustion dynamics irrespective of the operating conditions. It was found using RQA parameters that the deterministic nature becomes stronger with a decrease in [Formula: see text] and any deviation in intermediate values of [Formula: see text]. Additionally, RQA measures advocate that CA50 has more deterministic characteristics at higher engine speed while [Formula: see text] at lower engine speed. Strong coupling and synchronization between [Formula: see text] and CA50 is indicated by cross-recurrence plots and CPR index when engine operated with a comparatively richer mixture.

CFD simulation of heat transfer and airflows in an open refrigerated display cabinet

This paper uses CFD (Computational Fluid Dynamics) method to study the efficiency of the airflow curtain in an empty and full open refrigerated display cabinet. Numerical simulation results show that changing of the angle of the honeycomb can reduce the infiltration of warm ambient air into the refrigerator. It was established that the average intake air temperature in modified design decreased by 0.6 °C compared to the original design. The CFD model presented in the paper can be used to study airflows inside and to design and develop open-type refrigerated cabinets.

Predicting the energy and exergy performance of F135 PW100 turbofan engine via deep learning approach

In the present study, the effects of flight-Mach number, flight altitude, fuel types, and intake air temperature on thrust specific fuel consumption, thrust, intake air mass flow rate, thermal and propulsive efficiecies, as well as the exergetic efficiency and the exergy destruction rate in F135 PW100 engine are investigated. Based on the results obtained in the first phase, to model the thermodynamic performance of the aforementioned engine cycle, Flight-Mach number and flight altitude are considered to be 2.5 and 30,000 m, respectively; due to the operational advantage of supersonic flying at high altitude flight conditions, and the higher thrust of hydrogen fuel. Accordingly, in the second phase, taking into account the mentioned flight conditions, an intelligent model has been obtained to predict output parameters (i.e., thrust, thrust specific fuel consumption, and overall exergetic efficiency) using the deep learning method. In the attained deep neural model, the pressure ratio of the high-pressure turbine, fan pressure ratio, turbine inlet temperature, intake air temperature, and bypass ratio are considered input parameters. The provided datasets are randomly divided into two sets: the first one contains 6079 samples for model training and the second set contains 1520 samples for testing. In particular, the Adam optimization algorithm, the cost function of the mean square error, and the active function of rectified linear unit are used to train the network. The results show that the error percentage of the deep neural model is equal to 5.02%, 1.43%, and 2.92% to predict thrust, thrust specific fuel consumption, and overall exergetic efficiency, respectively, which indicates the success of the attained model in estimating the output parameters of the present problem.

Experimental investigations of methanol fumigation via port fuel injection in preheated intake air in a single cylinder dual-fuel diesel engine

Primary alcohols are emerging as promising alternative fuels for diesel engines. Dual-fuel engine operation with port injection (fumigation) of methanol has emerged as a novel concept for simultaneous reduction of particulate matter (PM) and oxides of nitrogen (NOx). This experimental study investigates the effect of intake air preheating on methanol-fumigated agricultural diesel engines. Methanol premixing ratio was kept constant at 50% (M50) for all test conditions. The experiments were performed at a constant speed of 1500 rpm at two intake temperatures of 40 °C and 80 °C, and engine load was varied from 1.25 to 5 bar brake mean effective pressure (BMEP). It was observed that intake air heating influenced the engine’s combustion, performance, and emission characteristics. Higher intake air temperature (M50, 80 °C) resulted in higher peak in-cylinder pressure and brake thermal efficiency (BTE) than the low-temperature case (M50, 40 °C). Higher intake air temperature compensated for the cooling effect due to evaporation of methanol caused by a shorter combustion duration, leading to more efficient energy conversion. Higher hydrocarbons (HC) and carbon monoxide (CO) emissions were observed in addition to lower nitric oxide (NO) emission for M50 vis-a-vis baseline diesel at all loads. The study concluded that intake air temperature significantly affects methanol-diesel dual-fuel engine characteristics and will be an important parameter requiring optimisation before large-scale methanol implementation in agriculture and transport sectors.

Influence of gasoline fuel formulation on lean autoignition in a mixed-mode-combustion (deflagration/autoignition) engine

Stoichiometric spark-ignition engines suffer efficiency penalties due to throttling losses at low loads, a low specific-heat ratio of the stoichiometric working fluid, and limits on compression ratio due to end-gas autoignition leading to undesirable knocking. Mixed-Mode Combustion (MMC) mitigates these shortcomings by using a lean working fluid where a spark-initiated pilot-stabilized deflagrative flame front is followed by controlled end-gas autoignition. This MMC study investigates the effects of initial conditions (intake air temperature, intake pressure, equivalence ratio, and intake oxygen fraction) on autoignition tendency of four gasoline-range fuels with varying properties and composition. The use of fuels with varying octane sensitivity (S) allowed exploring the importance of low-temperature heat release in triggering autoignition. Fuels with high S were less reactive for conditions that promote low-temperature chemistry (operation at high intake air pressure or without N2 dilution). Conversely, an Alkylate fuel with low S showed a greater autoignition resistance at operating conditions that were unfavorable for low-temperature chemistry. Next, the effect of residual gas composition on autoignition tendency of fuels was examined with a chemical-kinetics model. Among the various molecules in the residual gas, nitric oxide (NO) enhanced the low-temperature chemistry and increased the autoignition tendency most significantly. The fuels’ autoignition response to increasing NO amount corroborates the experimental observations. Next, the sequential autoignition of the end-gas was assessed to be less impacted by thermal stratification because of lean mixtures showing relatively less low-temperature chemistry, when compared to stoichiometric mixtures. Next, the effect of changing equivalence ratio on the autoignition was found to be similar for all fuels, regardless of their S. With changing intake air temperature, the response of fuels’ autoignition tendency depended on the dilution level used. At high dilution (i.e. low intake [O2]), fuels’ reactivity increased with increasing intake air temperature. In contrast, for operation without dilution, the autoignition tendency of the low-S Alkylate fuel decreased with increasing intake air temperature, while that of high-S High Cycloalkane fuel still increased with increasing intake air temperature. In conclusion, conventional octane metrics (RON and MON) have utility in assessing the autoignition tendency under lean MMC operation. Moreover, the fuel requirements for MMC align with that of stoichiometric operation: i.e., high RON and high S fuels are desirable for stable non-knocking operation.

Effect of the Air Flow on the Combustion Process and Preheating Effect of the Intake Manifold Burner

Diesel engines show poor performance and high emissions under cold-start conditions. The intake manifold burner is an effective method to increase the intake air temperature and improve engine performance. In this paper, a visualization system was employed to investigate the combustion process of the intake manifold burner. The effects of diesel flow rate and airflow velocity on combustion performance were investigated. The combustion process of the intake manifold burner showed four stages: preparing stage A, rapid development stage B, steady-development stage C, and stable stage D. Flame stripping was found in stages C and D, presenting the instability of the combustion process. With the increase in air flow velocity from 1.4 m/s to 3.0 m/s, the flame stripping was enhanced, leading to the increasing combustion instability and regular flame penetration fluctuations. The average temperature rise and combustion efficiency increased with the increasing diesel flow rate, indicating the combustion enhancement. Comparison of temperature rise and combustion efficiency under 2.0 m/s and 10.0 m/s showed that stronger cross wind enhances the heat convection, improving the temperature uniformity and combustion efficiency.

Development of an Air-Cooled Induction Manifold for Diesel Engines in Hot and Humid Climate

Abstract Extreme weather conditions in the Gulf, Qatar, have been taken as an example in this study, tend to be hot and humid mostly throughout the year, especially in the summer. Such weather negatively affects the performance and emissions of all combustion engines, in particular diesel engines. In this work, a modified air-conditioning system was designed for controlling the inlet air temperature and humidity of a naturally aspirated single-cylinder diesel engine. The study investigated the effect of running the engine at different controlled inlet air temperatures on the engine performance and emission characteristics. It was found that running the diesel engine at 20 °C inlet air temperature compared with 45 °C, the average ambient air temperature during summer in Qatar could increase the in-cylinder peak pressure by 10%, and the volumetric efficiency of the engine by 8.5%. Moreover, the air-to-fuel (A/F) ratio has increased by 27.5% with 20 °C compared with 45 °C, while a minor effect was observed on the specific fuel consumption. For the emissions, there was a considerable reduction rate in NOx emissions with about 83% at 20 °C as well as a 50% reduction in hydrocarbon (HC) emissions compared with 45 °C. Furthermore, the smoke emission has decreased by 40% at the engine full load. It was also proved that using the air-conditioning system of a vehicle to cool the intake air temperature is visible, as the net gained the power of the engine has increased by 14.5% when running at 20 °C compared with 45 °C.

Simulation and experimental investigation of an organic phase change material-based air-cooling system for industrial applications in the hot climate

ABSTRACT This work proposes a novel cooling system of the inlet air for industrial applications in the hot climates using organic phase change material. This cooling system consists of an inductive fan, an underground heat exchanger including double pipe phase change material. A three-dimensional transient simulation was developed to predict cooling capacity (temperature drop) using the analytical solution method within the MATLAB open-source code software. A prototype of the system was designed, built and tested in laboratory conditions to validate the modeling results. The experimental setup shows an average temperature reduction of 6°C in the air-cooling system in nine working hours, which matches with the simulation results with a variance of less than 2%. Further simulations demonstrated that an industrial scale could reduce the average temperature of intake air to 10°C in 7 hours working. The offline analysis proved a significant energy conservation opportunity in power plants. This study showed that energy performance and power generation of an industrial-scale gas turbine can be improved by 1% and 1.2 MW, respectively.

Пуск дизельного двигателя 1Ч9,5/8,0 путем принудительной подачи предварительно разогретого воздушного заряда

The use of small-sized air-cooled diesel engines as part of mobile units for operation in the harsh climatic conditions of the Arctic is a rather difficult task. As the ambient temperature decreases, the temperature at the compression stroke end, which is necessary for the appearance of the first flashes in the diesel cylinder, decreases significantly. At the ambient temperature of minus 60°C, start of a diesel engine becomes impossible. The stage of the appearance of the first flashes is very important for the subsequent spin-up of the crankshaft and the onset of a diesel engine independent operation on fuel without the involvement of auxiliary starting devices. The article proposes a method and device for increasing the temperature in the combustion chamber at the compression stroke end. The results of a diesel engine start at various negative ambient temperatures are given. The regularities of the dynamics of starting a diesel engine 1Ch9.5/8.0 and the dependence of the crankshaft speed during start-up on the ambient temperature is established. The rational range of intake air temperature required for the diesel engine start-up by the proposed method at an ambient temperature from minus 50 to minus 60°C is determined. The proposed method and device can be applied in similar diesel engines with a smaller working volume.

Optimization of Marine Two-Stroke Diesel Engine Based on Air Intake Composition and Temperature Control

The influence of gas intake temperature, composition and the volume concentration of each gas component on diesel engine combustion, emission and the output power was studied by building a calculation model of the B&W 6S35ME-B9 marine two-stroke low-speed diesel engine, followed by a comprehensive optimization exploration. The results showed that under 295 K and 18.5% O2 of intake gas, the engine’s NOx emission is only 4.5 g/kWh and reduced to 58% from the normal air gas intake condition. Moreover, their power output is very similar. In addition, the effect of CO2 or H2O added into the intake of the diesel engine on the performance of the diesel engine can be compensated by reducing the intake temperature. At the intake temperature of 295 K, the engine’s NOx emission with 20.58% O2, 77.42% N2 and 2% H2O is 8.62 g/kWh, and 9.06 g/kWh under 20.79% O2, 78.21% N2 and 2% CO2. It is lower than 11.77 g/kWh, which is under normal intake conditions (315 K, 21%O2 and 79%N2). The power output is also similar to the normal intake condition. Therefore, the comprehensive optimization of gas intake temperature, composition and concentration can effectively optimize the diesel engine’s performance in terms of combustion, emission and power output. The research results have an important reference value for the optimization of diesel engine performance.

Simulation of innovative hybridizing M-cycle cooler and absorption-refrigeration for pre-cooling of gas turbine intake air: Including a case study for Siemens SGT-750 gas turbine

Higher compressor intake-air temperature not only significantly reduces the performance of the gas turbine (GT), but also increases the NOx emissions. Absorption (AB) refrigeration, which is powered by heat, is a promising option for cooling GT intake air. M-cycle technology is a unique water-based indirect evaporative cooler (IEC) providing sub wet-bulb temperature. In novel hybrid pre-cooler, the air is cooled down to near dew-point temperature by the M-cycle first and then further cooled by the AB. Both AB and M-cycle coolers consume very little electricity and the main required sources (heat for AB refrigeration and water for the M-cycle IEC) are provided by waste heat from GT and condensed water from AB meaning almost zero-energy pre-cooler for GT intake air. The dependency of the intake mass flow and GT power output on the intake air temperature is first identified and correlated using experimental data provided by Siemens company, and then the required physical/mathematical modelling is presented and developed using Engineering Equation Solver. Finally, the GT performance is comprehensively discussed for a wide range of climate conditions when the AB and M-cycle work solely or jointly as a GT intake air pre-cooler. The hybrid pre-cooler was found to be a cost-effective way to boost the GT power output by 29%, however, this enhancement for GT using AB refrigeration and M-cycle IEC was around 17% and 15% in average respectively.

Effects of intake air conditions and micro-pilot (MP) injection timing on micro-pilot dual fuel (MPDF) combustion characteristics in a single cylinder optical engine

The effects of intake air conditions and micro-pilot injection timing on the characteristics of micro-pilot dual fuel combustion were examined to enhance the combustion stability in marine engines. A minimum amount of diesel fuel was injected as the ignition source, and most of the fuel energy was obtained from methane gas. First, the intake air flow rate was varied. In addition, the methane gas flow rate and micro-pilot injection timing were changed depending on the intake air flow rate. Second, the micro-pilot injection timing was varied under intake air temperatures of 35 °C and 55 °C. The intake air and methane gas flow rates were maintained. Results indicated that increasing the intake air and methane gas flow rates promoted autoignition in the end-gas region. Nevertheless, the standard deviation of the peak cylinder pressure was within 3.1 bar. Under the intake air temperature of 35 °C, advancing and retarding the micro-pilot injection led to misfiring, which increased the standard deviation of the peak cylinder pressure to 10.2 bar and 9.6 bar, respectively. Knocking combustion was occurred when the micro-pilot injection was retarded under the intake air temperature of 55 °C. This phenomenon increased the standard deviation of the peak cylinder pressure to 6.9 bar. Premixed ignition in the end-gas region combustion corresponded to the optimal engine operating conditions for marine engines because of the low combustion variation even under high cylinder pressures of approximately 170 bar to 220 bar. However, high NOx emissions occurred under these conditions.

Off-design modeling of a microturbine combined heat & power system

There is increasing interest in decision support software tools that evaluate the techno-economic potential of distributed energy system technologies for deployment in combined heat and power (CHP) applications, such as commercial buildings, microgrids, and connected communities. This trend is particularly evident among end-users looking to integrate renewable resources with more traditional CHP technologies for on-site generation and enhanced resiliency. However, many of these software tools do not account for part-load and off-design characteristics of prime mover and heat recovery equipment, resulting in lower accuracy for both the optimal selection and sizing and the economic value proposition of integrated hybrid renewable energy-CHP systems. Microturbine technology is an attractive distributed energy resource whose performance is sensitive to both part-load and off-design (i.e., excursions of ambient conditions away from the design point temperature and pressure) operating conditions but is widely unreported. In the present work, we address this deficiency by developing a detailed, thermodynamic model of a commercial 200 kW microturbine CHP system and paramaterizing results for incorporation into the Renewable Energy Optimization (REopt) tool developed by the National Renewable Energy Laboratory. The details of the microturbine model, including model benchmarking and validation, are presented. Microturbine off-design modeling includes part-load analysis, assessment of ambient sensitivities, and mapping heat recovery heat exchanger response to hot water grade requirements. The model is then exercised in several illustrative examples to depict the numerous factors which alter electric power, electric efficiency, and hot water recovery. Model results show, for example, predictions of a 4 percentage point electric efficiency range occurring between intake air temperatures of -18 to 50 °C. Likewise, the model closely predicts the 25 % loss in heat recovery while at -18 °C and the 8 % gain in heat recovery while at 35 °C. An additional case shows how heat recovery may increase or decrease by 9.5 % of the design value when changing the return water temperature plus-or-minus 22 °C. In particular, the impact of ambient conditions on best-possible microturbine performance is conveyed through hourly simulations of the system subjected to the weather of different geographic locations within the United States. • A model of a 200 kW microturbine configured for hot water recovery is developed. • Part-load modeling approach and simulation results for both electric efficiency and waste heat recovery are detailed. • Off-design performance as functions of ambient temperature and pressure is explored. • Heat recovery performance maps as functions of return and supply hot water temperatures are developed.

Experimental study on controlled hot surface assisted compression ignition (HSACI) in a naturally aspirated single cylinder gas engine

Homogeneous charge compression ignition (HCCI) promises low [Formula: see text] emissions and high efficiency due to fast combustion at low temperatures. However, the control of combustion timing represents a serious challenge due to the lack of dedicated ignition control parameters. This challenge is addressed in this work by means of a hot surface ignition (HSI) system, whose core element consists of a shielded, electrically heated ceramic glow plug. In this approach, termed as hot surface assisted compression ignition (HSACI), a small portion of mixture is thought to ignite in the vicinity of the shielded glow plug and to subsequently propagate to the main combustion chamber in order to initiate bulk-gas auto-ignition. Adjusting the hot surface temperature enables to either advance or retard the onset of combustion and thus, allows to control combustion timing. This paper presents experimental results of initial engine trials, using the HSACI concept in a naturally aspirated single cylinder natural gas engine. Measurements were conducted at a constant engine speed of 1400 l/min and include intake air temperatures in the range of 150–175°C and relative air-fuel ratios ([Formula: see text]) from 2.0 to 2.8. Results show that the HSI system enables combustion under conditions, which do not allow for pure HCCI operation. Moreover, the combustion timing can be actively controlled within certain limits by changing the HSI temperature. Increasing cycle-to-cycle variations limit stable operation at lower temperatures, while a transition to pure HCCI is found at intake temperatures beyond 170°C. The applicable [Formula: see text] range is limited by knocking or uncontrolled combustion toward the rich side and instable operation toward the lean side. Loss analysis points out that wall heat flow and imperfect combustion represent the dominant loss mechanisms. Heat release analysis reveals two pronounced phases, indicating initial flame propagation and subsequent auto-ignition similar to spark assisted compression ignition (SACI).