NOx emission from a two-stroke ship engine: Part 2 – Laboratory test

International regulations force ship owners to monitor the NO_x emission from engines during sea operational use of ships, but standard equipped engine rooms has not installed any measurement equipment to analyze of exhaust gases. According to these regulations, we proposed a simple method to estimation of NO_x emission without direct measurement, based on the measurements of working engine parameters. In this paper, we present the effect of laboratory test to verification adequacy of the developed model. In this aim, we carried out tests on the two-stroke, one-cylinder, and loop scavenged diesel engine. During tests the engine operated with the various rotational speed, load, and changing air/fuel equivalence ratio. The comparison of the results of calculations with conducted tests showed the estimation errors in intervals 1.8% to 11% in dependence from the substitute molar compositions of fuels.     

Evaluation of Miller cycle and fuel injection direction strategies for low NOx emission in marine two-stroke engine

A full cycle computational fluid dynamics (CFD) simulation model has been established to study the effect of injection direction and exhaust valve close (EVC) timing on performance and emissions for a slow speed marine engine. In order to find more combustion details, the model was coupled with simplified chemical kinetics mechanism. Meanwhile the paper presents the optimization results combining variable injection direction with late exhaust valve closing (LEVC). The results indicate that the consistency of injection direction and flow direction has an important impact on fuel economy. To improve fuel consumption, the injection direction must be carefully adjusted within certain limits. A certain degree of sacrifice in fuel economy is reflected on the transient calculation using the LEVC strategy. However, significant improvement in NOx (nitrogen oxides) emission can be achieved accordingly. With optimized EVC timing and injection direction, lower NOx emission can be realized with no penalty of fuel consumption.     

Combustion and emission characteristics of a two-stroke diesel engine operating on alcohol

Though, as a renewable energy resource, alcohol fuel has many advantages in China, it is difficult for diesel engines to operate on alcohol due to its low cetane number and high latent heat of vaporization. This paper proposes an approach to its ignition problem by combining internal exhaust gas recirculation (EGR) with injection of small diesel fuel. Based on this approach, a two-stroke single-cylinder diesel engine was developed. Preliminary studies demonstrated that the engine can run on alcohol with almost zero level of smoke and low exhaust gas temperature, and that the engine operating on alcohol has lower nitrogen oxide (NO_x) emissions and 2–3% higher effective thermal efficiency than that operating on diesel fuel in moderate and high load zones.     

Development of a hot-surface-ignition hydrogen injection two-stroke engine

A 3-cylinder, 1100 cc two-stroke gasoline engine was converted into a hot-surface-ignition hydrogen injection diesel engine for a new hydrogen car named Musashi 5. This engine had a compression ratio of 12:1, and the high pressure hydrogen at 6 MPa was injected into an open combustion chamber near the TDC. In practice, it showed some problems in terms of the high pressure liquid hydrogen pump, the hot surface ignition and efficient combustion. Efforts were made to solve the problems, and the results were as follows: (1) a high pressure pump was obtained through the precise finish on the sliding surfaces of the barrel and plunger, and by the combination of appropriate material and dimensions; (2) a gentle diesel ignition was attained by blowing hydrogen gas onto the platinum wire at 1000°C from a close location; (3) the mixture formation was improved, and the maximum power equivalent to 125% of gasoline was obtained by a proper selection of combustion chamber shape, number of injection nozzles, direction of injection, etc.     

An analytic study of applying Miller cycle to reduce NOx emission from petrol engine

An analytic investigation of applying Miller cycle to reduce nitrogen oxides (NO_x) emissions from a petrol engine is carried out. The Miller cycle used in the investigation is a late intake valve closing version. A detailed thermodynamic analysis of the cycle is presented. A comparison of the characters of Miller cycle with Otto cycle is presented. From the results of thermodynamic analyses, it can be seen that the application of Miller cycle is able to reduce the compression pressure and temperature in the cylinder at the end of compression stroke. Therefore, it lowers down the combustion temperature and NO_x formation in engine cylinder. These results in a lower exhaust temperature and less NO_x emissions compared with that of Otto cycle. The analytic results also show that Miller cycle ratio is a main factor to influence the combustion temperature, and then the NO_x emissions and the exhaust temperature. The results from the analytic study are used to analyse and to compare with the previous experimental results. An empirical formula from the previous experimental results that showed the relation of NO_x emissions with the exhaust temperature at different engine speed is presented. The results from the study showed that the application of Miller cycle may reduce NO_x emissions from petrol engine.     

The control of a free-piston engine generator. Part 1: Fundamental analyses

Free-piston engines are under investigation by a number of research groups due to potential fuel efficiency and exhaust emissions advantages over conventional technology. The main challenge with such engines is the control of the piston motion, and this has not yet been fully resolved for all types of free-piston engines. This paper discusses the basic features of a single piston free-piston engine generator under development at Newcastle University and investigates engine control issues using a full-cycle simulation model. Control variables and disturbances are identified, and a control strategy is proposed. It is found that the control of the free-piston engine is a challenge, but that the proposed control strategy is feasible. Engine speed control does, however, represent a challenge in the current design.     

Experimental investigation of combustion characteristics and NOx emission of a turbocharged hydrogen internal combustion engine

In order to alleviate the contradictions of increasingly prominent environmental pollution, greenhouse gas emissions and oil resource security issues, the search for renewable and clean alternative energy sources is getting more and more attention. Hydrogen energy is known as a future energy source because of its safety, reliability, wide range of resources and non-polluting products. Hydrogen internal combustion engine combines the technical advantages of traditional internal combustion engines and has comprehensive comparative advantages in terms of manufacturing cost, fuel adaptability and reliability. It is one of the practical ways to realize hydrogen energy utilization. In this paper, the combustion characteristics and NOx emission of a turbocharged hydrogen engine were investigated using the test data. The results showed the combustion duration (the crank angle of 10%–90% fuel burned) at 1500 rpm and 2000 rpm was equal and the combustion duration is much bigger than the other loads when the BMEP is 0.27 MPa. The reason is the effect of the turbocharger on the gas exchange process, which will influence the combustion process. The cylinder pressure and pressure rise rate were also investigated and the peak pressure rise rate was lower than 0.25 MPa/°CA at all working conditions. Moreover, the NOx emission changed from 300 ppm to 1200 ppm with engine speed increasing and the maximum value can reach to 7000 ppm when the equivalence ratio is 0.88 at 2500 rpm, maximum brake torque. The NOx emission shows different changing tendencies with different working conditions. Finally, these conclusions can be used to develop controlling strategies to solve the contradictions among power, brake thermal efficiency and NOx emission for the turbocharged hydrogen internal combustion engines.     

Numerical analysis of combustion and transient heat transfer processes in a two-stroke SI engine

A zero-dimensional model is presented to simulate the transient processes occurring within a two-stroke SI engine. A two zone combustion model, with a spherically expanding flame front originating from the spark location, is applied. The model is numerically solved using the network simulation model which allows coupling the combustion model with a heat transfer model where both radiant and convective heat contributions have been taken into account for the in-cylinder gases. The boundary conditions for this model are the convective heat transferred to the cooling medium. A gas mixture model has been used to obtain the influence of working fluid properties on combustion development.     

Effect of injection parameters on the reduction of NOx emission in neat bio-diesel fuelled diesel engine

This article has been retracted     

Modeling and optimization of the NOx emission characteristics of a tangentially fired boiler with artificial neural networks

The present work introduces an approach to predict the nitrogen oxides (NOx) emission characteristics of a large capacity pulverized coal fired boiler with artificial neural networks (ANN). The NOx emission and carbon burnout characteristics were investigated through parametric field experiments. The effects of over-fire-air (OFA) flow rates, coal properties, boiler load, air distribution scheme and nozzle tilt were studied. On the basis of the experimental results, an ANN was used to model the NOx emission characteristics and the carbon burnout characteristics. Compared with the other modeling techniques, such as computational fluid dynamics (CFD) approach, the ANN approach is more convenient and direct, and can achieve good prediction effects under various operating conditions. A modified genetic algorithm (GA) using the micro-GA technique was employed to perform a search to determine the optimum solution of the ANN model, determining the optimal setpoints for the current operating conditions, which can suggest operators’ correct actions to decrease NOx emission.     

某艇用柴油机改二甲醚发动机性能与排放特性分析

以一台4缸艇用增压柴油机为研究对象,基于STAR-CD软件,计算了该柴油机燃用二甲醚(DME)时的缸内压力、温度与NOX排放的变化情况,并与其燃用柴油时情况进行了对比。分析了在不同负荷与不同喷孔直径下燃用DME时的NOX排放特性。结果表明,该柴油机燃用DME后,动力性能降低幅度甚微,基本在2%以内,其NOX的排放比燃用柴油要低15%左右,为艇用DME发动机的开发提供了依据。     

Modeling of combustion characteristics and NOx emission in highly preheated and diluted air combustion

The gas diffusion combustion in a regenerative furnace with highly preheated and diluted air has been numerically investigated in this paper. The highly preheated air combustion possesses high combustion intensity and high level temperature, but the NO_x emission also has an unwanted high level. Decreasing the oxygen concentration in the highly preheated air could decrease the NO_x emission and improve the uniformity of temperature distribution in the furnace. The combustion characteristics of highly preheated and diluted air combustion have been studied, including temperature distribution, soot formation, OH radical distribution, as well as NO_x emission. The influence of the preheated air temperature, the oxygen concentration, and the air diluent has also been investigated. The optimal combinations of the preheated air temperature and the oxygen concentration have been predicted in the case of flue gas recirculation, which could provide the highest possible temperature in the furnace while keeping the NO_x emission lower than the permitted value. © 1998 by John Wiley & Sons, Ltd.     

NOx emission from high-temperature air/methane counterflow diffusion flame

The objectives of the present study are to measure NO_x emission of counterflow diffusion flame, to compare the findings with numerical results, and finally to demonstrate efficacious effect of high-temperature air with low concentration of oxygen on NO_x emission. Recently, high-temperature air with low concentration of oxygen is used for various industrial furnaces, resulting high efficiency and low emission of pollutants. Since high-temperature air increases NO_x emission and air with low concentration of oxygen decreases it, these effects are competitive. Measurement and computation were conducted to clarify these two effects by use of counterflow diffusion flame. Since it is difficult to employ very high temperature over 1100 K in a laboratory-scale apparatus, a quantitative agreement between experimental and numerical results was confirmed first, and then a numerical approach was used to obtain a larger effect of low oxygen to reduce NO_x emission. In the experiments, the methane concentration is changed from 10 to 30 vol% diluted by nitrogen, oxygen from 10 to 21 vol%, and air temperature from room temperature to 1100 K. The total amount of NO_x sufficiently agreed between experimental and numerical results, although NO and NO₂ could not be separated. By the numerical method, it was found that NO_x emission from the counterflow diffusion flame of high-temperature low-oxygen air of 1500 K and 5% oxygen is comparable with that of room-temperature air of 21% oxygen.     

柴油机试验中颗粒物排放的后处理方法研究

针对柴油机在试验台试验过程中产生的大量有害废气,设计了一种低成本、结构简单的过滤装置。采用多组不锈钢网、荷电微粒过滤技术及燃媒催化再生技术来减少废气中微粒的排放量,以降低铁路牵引用柴油机台架试验对大气的有害排放。     

A liquid hydrogen car with a two-stroke direct injection engine and LH2-pump

Objectives for the practical application of hydrogen cars are (i) engine-output increase (power-up), suppression of abnormal combustion, and NO_x reduction; (ii) the development of a low cost liquid hydrogen-(LH₂) tank having high thermal insulation; and (iii) the development of a method to supply fuel from the LH₂-tank to the engine. We have developed a hydrogen car system consisting of a LH₂-tank-LH₂-pump-injector to inject high pressure and low temperature hydrogen gas into a two-stroke engine that is capable of meeting all the above-mentioned requirements except (ii). The system was then applied to a mini-car equipped with a 0.551, engine. The performance of the car has demonstrated the above-mentioned capabilities from the engine dynamometer and road tests.     

微型燃气轮机燃烧室NOx排放性能实验研究

作为微型燃气轮机的核心部件之一,燃烧室性能的优劣将直接影响微型燃气轮机的整体性能。随着环保意识的增强和环保法规的日益严格,控制燃烧室污染物的排放业已成为一个重要课题。以一微型燃气轮机燃烧室为对象进行了热态条件下NOx排放性能的实验研究。实验结果表明：随着过量空气系数的增加,NOx的排放浓度呈下降趋势;燃烧区温度的升高以及在高温区停留时间变长,NOx生成量大大上升;在较高负荷工况下,NOx的排放量较小。     

Control of backfire and NOx emission reduction in a hydrogen fueled multi-cylinder spark ignition engine using cooled EGR and water injection strategies

The experimental study was carried out on a constant speed multi-cylinder spark ignition engine fueled with hydrogen. Exhaust gas recirculation (EGR) and water injection techniques were adopted to control combustion anomalies (backfire and knocking) and reduce NOx emission at source level. The experimental tests were conducted on the engine with varied EGR rate (0%–28% by volume) and water to hydrogen ratio (WHR) (0–9.25) at 15 kW load. It was observed from the experiments that both the strategies can control backfire effectively, but water injection can effectively control backfire compared to EGR. The water injection and EGR reduce the probability of backfire occurrence and its propagation due to the increase in the requirement of minimum ignition energy (MIE) of the charge, caused mainly due to charge dilution effect, and reduction in flame speed respectively. The NOx emission was continuously reduced with increase in EGR rate and WHR, but at higher rates (of EGR and WHR), there was an issue of stability of engine operation. It was found from the experimental results that at 25% EGR, there was 57% reduction in NOx emission without drop in brake thermal efficiency whereas, with WHR of 7.5, the NOx emission was reduced by 97% without affecting the efficiency. The salient point emerging from the study is that water injection technique can control backfire with ultra-low (near zero) NOx emission without compromising the performance of the hydrogen fueled spark ignition engine.     

Comparison of the combustion and emission characteristics of NH3/NH4NO2 and NH3/H2 in a two-stroke low speed marine engine

As a marine engine fuel of great concern, ammonia needs to be mixed with another high reactive fuel to improve its combustion performance. In this work, the combustion performance of NH₃/NH₄NO₂ and NH₃/H₂ was compared under different boundary conditions (excess air coefficient, initial temperature, pressure and mixing ratio). The numerical simulation of compression combustion is carried out under different power loads. The addition of ammonium nitrite decreases the ignition requirement of ammonia and shortens the ignition delay time of the mixture fuel. The boundary conditions of compression ignition can be reduced by mixing hydrogen and mixing ammonium nitrite, but it is not enough to achieve compression ignition under NH₃/H₂ mode. The addition of 30% ammonium nitrite can reduce the intake temperature to 300–360 K, which makes the compression ignition of the mixed fuel feasible. Meanwhile, in order to reduce the high in-cylinder combustion pressure and improve the combustion performance of the mixed fuel, the fuel injection strategy was proposed to achieve constant combustion pressure of 30 MPa under the premise of less power loss, which is a potential solution for the combustion of ammonia fuel.     

Flame structure and NOx emission characteristics in a single hydrogen combustor

In this study, the effects of fuel-induced swirl number on the flame structure and NOx emissions are observed. A tube-type nozzle with four fuel injection holes is used. The fuel injection holes are located away from the centerline of the nozzle to induce a low swirl effect in the flow. First, the flame structure changes with the fuel-induced swirl number, separating into four small flames in the high-swirl region; the flames are classified into three types. Subsequently, NOx emissions decrease with an increase in the fuel-induced swirl number. However, this shows a stepwise discontinuous change rather than a gradual change. The NOx emission is linearly proportional to the residence time of the combustion gas, which is calculated using the flame volume and flame structure. In conclusion, the change in the flame structure by the fuel-induced swirl is a decisive factor in the reduction of the NOx.