Start Of Combustion Research Articles

The thermal and auto-ignition performance of a homogeneous charge compression ignition engine fuelled with diethyl ether and ethanol blends

Abstract This study aims to numerically investigate the thermal and auto-ignition performance of a Homogeneous Charge Compression Ignition (HCCI) engine fuelled with diethyl ether and ethanol blends at different inlet air temperatures and lambda values. In this study, DEE and DEE/ethanol blends with different volume percentages, such as 85% DEE/15% ethanol (D85E15) and 70% DEE/30% ethanol (D70E30) was used as test fuels. A four-stroke single-cylinder HCCI engine was designed to use reduced fuel chemistry to create a zero-dimensional single-zone model. The single-zone combustion model was developed with the first law of thermodynamics as a differential form. The inlet air temperature ranged from 360 K to 420 K at 15 K intervals, and the lambda ranged from 1.5 to 2.5 at 0.25 intervals to evaluate the combustion control in the HCCI engine. A numerical study was carried out at an engine speed of 1200 rpm. The numerical validation model results were well agreed with reported experimental results, and the significant trends of the combustion phases were varied with a minimum error of 5%. The numerical results show that the in-cylinder pressure and heat release rate are decreased for all test fuels with the increasing lambda. The combustion phase was found to be advanced, and the combustion duration was expanded with increasing inlet air temperature. Increasing the ethanol proportion in the test fuel delayed the start of combustion. For D85E15 and D70E30 at lambda of 2 and inlet air temperature of 420 K, the indicated mean effective pressure was increased by about 12.6% and 6.10 bar. Furthermore, with DEE and D85E15 at a lambda of 2, the indicated thermal efficiency was increased by approximately 11.4% and 49.17%. It is concluded that the combustion and performances characteristics for the HCCI engine are significantly affected by DEE and ethanol fuel blends.

Varying Ignition Quality of a Fuel for a HCCI Engine Using a Photochemically-Controlled Additive: The Development of a ‘Smart’ Fuel

This study examines the possibility to provide control over ignition timing in a homogeneous charge compression ignition engine (HCCI) using a fuel additive whose molecular structure can be adapted upon exposure to UV light. The UV adapted molecule has a greater influence on retarding ignition than the original molecule, hence the ignition time can be modulated upon expose to UV light. The new fuel is referred to as a ‘smart fuel’. The fuel additive is in the form of 1,3-cyclohexadiene (CHD), upon UV exposure it undergoes electro-cyclic ring opening to form 1,3,5-hexatriene (HT). Various solutions of iso-octane, n-heptane and CHD have been irradiated by UV light for different amounts of time. CHD to HT conversion was examined using gas chromatography coupled with mass spectrometry. A primary reference fuel (PRF) mixture of 90% iso-octane and 10% n-heptane was used as a baseline in an optically accessible combustion chamber in a large bore, single cylinder compression ignition engine. The engine was operated in HCCI mode, using early injection to provide homogeneous mixture and utilized heated and compressed air intake. Following this a PRF with 5% CHD was used in the engine. A PRF with 5% CHD was then irradiated with UV light for 240 min, resulting in a PRF mixture containing 1.72% HT, this was then used in the engine. The HT containing PRF had a much later start of combustion compared with the CHD containing PRF, which in turn had a later start of combustion compared with the PRF baseline. This study has successfully validated the concept of using a photo-chemical ‘smart’ fuel to significantly change the ignition quality of a fuel in HCCI mode combustion and demonstrated the concept of on-board ‘smart fuel’ applications for ICE.

Optimization of diesel engine performance and emission parameters of Karanja biodiesel-ethanol-diesel blends at optimized operating conditions

This study reviews Karanja biodiesel, ethanol and diesel blending in context of Indian subcontinent and also focuses on its effects on engine’s performance, emission and combustion responses. Experimentations carried out on four stroke single cylinder diesel engine at constant speed 1500 rpm and injection pressure 210 bar. The four input parameters as Injection angle, Compression ratio, Blend % and loads varied to obtain engine responses as Brake thermal efficiency, Brake specific fuel consumption, Exhaust gas temperature, Carbon dioxide, Carbon monoxide, Nitrogen Oxide and hydrocarbon. Taguchi method was applied to optimize the trials using L9 orthogonal array and to get main effects S/N ratio curves, for optimal combination of input parameters to response. The ANNOVA was used to establish the contribution of input parameters to responses. Further single combination of input parameters for all seven responses as Injection Angle 19°CA bTDC, Compression ratio 18, Krishna 30 (fuel blend) and 50% load was obtained by Gray Relational Analysis. Experimentation revealed marginal reduction of brake thermal efficiency about 2%, Brake specific fuel consumption higher by 3%, Exhaust gas temperature increases by 3%, Carbon dioxide increases by 0.86%, hydrocarbon decreases by 12 PPM, carbon monoxide and Nitrogen oxide reduced by 0.029% and 8% respectively when compared with diesel at full load. The combustion parameters as Cylinder pressure, Ignition delay, Combustion duration, Start of combustion, End of combustion, Rate of pressure rise, Mean effective pressure and Net heat release rate were observed at full load, also support optimal combination of input parameters.

Explorations of the impacts on a hydrogen fuelled opposed rotary piston engine performance by ignition timing under part load conditions

High power density of opposed rotary piston (ORP) engines provides a possibility for the applications to hybrid vehicles. Under real driving conditions, internal combustion engines as the power sources of hybrid vehicles run under part load conditions in majorities of operation time. Hydrogen applications in internal combustion engines will promote zero-carbon travel, contributing to alleviating global warming. In this investigation, 3D numerical simulations were conducted to explore the performance of an ORP engine fuelled with hydrogen under part load and various ignition timing conditions. The results indicated that peak in-cylinder pressure and corresponding crank angle (CA) changed slightly within the early ignition range of −20.85º CA~ −14.23º CA; peak in-cylinder pressure was decreased significantly by late ignition. Heat release rates were more sensitive to late ignition than early ignition. Start of combustion, combustion phase, and combustion durations presented minor impacts by early ignition and engine loads. Ignition timing of −20.85º CA~ −11.06º CA showed limited impacts on indicated mean effective pressure and indicated power over individual intake manifold pressure. Indicated thermal efficiency was around 40% for the ignition timing of −20.85º CA~ −11.06º CA over the intake manifold pressure of 0.8 bar; indicated thermal efficiency drop caused by ignition timing of −8.33º CA was higher than 7% compared with optimal conditions. Heat loss by cylinder walls in proportions of fuel energy was lower than 25%, 20%, 18% for the intake manifold pressure of 0.4 bar, 0.6 bar, 0.8 bar respectively. Energy loss by the exhaust was higher than 41% for all the scenarios, with the maximum value being approximately 57%. Nitrogen oxides (NOx) emission factors were higher than 11 g (kW h)−1, and they were increased significantly by early ignition.

Effect of gasoline additive on combustion and emission characteristics of an n-butanol Partially Premixed Compression Ignition engine under different parameters

The experiments were conducted on a modified two-cylinder diesel engine to investigate the effects of excess-air coefficient (λ) and intake temperature (Tin) of different blending ratios (volume ratio of gasoline in the blends) on the combustion and emission characteristics of a Partially Premixed Compression Ignition (PPCI) engine. The results show that with the increase of gasoline blending ratio, the peak in-cylinder pressure (Pmax), the peak in-cylinder temperature (Tmax) and the peak heat release rate (HRRmax) of four test fuels all increase first and then decrease. When gasoline volume fraction is 10%, HC and CO emissions are the lowest. In addition, intake temperature (Tin) has a significant effect on the n-butanol/gasoline PPCI engine. With the increase of Tin, the in-cylinder Pmax and HRRmax of four test fuels gradually increase, the combustion phase advances and HC and CO emissions decrease, while NOx emissions increase slightly. Furthermore, as λ increases, the Pmax, Tmax and HRRmax of the four test fuels show monotonously reducing trend. At the same time, mixture concentration has basically no effect on start of combustion (CA10), the combustion duration (CD) gradually extends, and HC and CO emissions increase.

Vibration analysis and combustion parameter evaluation of CI engine based on Fourier Decomposition Method

As a non-intrusive method for engine working condition detection, the engine surface vibration contains rich information about the combustion process and has great potential for the closed-loop control of engines. However, the measured engine surface vibration signals are usually induced by combustion as well as non-combustion excitations and are difficult to be utilized directly. To evaluate some combustion parameters from engine surface vibration, the tests were carried out on a single-cylinder diesel engine and a new method called Fourier Decomposition Method (FDM) was used to extract combustion induced vibration. Simulated and test results verified the ability of the FDM for engine vibration analysis. Based on the extracted vibration signals, the methods for identifying start of combustion, location of maximum pressure rise rate, and location of peak pressure were proposed. The cycle-by-cycle analysis of the results show that the parameters identified based on vibration and in-cylinder pressure have the similar trends, and it suggests that the proposed FDM-based methods can be used for extracting combustion induced vibrations and identifying the combustion parameters.

Effect of post-injection strategy on greenhouse gas emissions of natural gas/diesel dual-fuel engine at high load conditions

In this study the effect of two diesel injection strategies named main-post and pre-main-post on natural gas/diesel dual-fuel (NDDF) combustion at high load conditions is investigated. In the main-post diesel injection strategy, part of diesel is injected after the main injection in the late expansion stroke (post-injection). In the pre-main-post injection strategy, part of diesel fuel is injected before main injection in the early compression stroke (pre-injection) and part of diesel fuel is injected after main injection in the late expansion stroke. The results revealed that the main-post diesel injection strategy did not change the start of combustion compared to single injection strategy. However, the pre-main-post injection strategy significantly increased the cylinder pressure and advanced the start of combustion. The maximum measured indicated fuel efficiencies (IFE) of NDDF engine with both single and pre-main diesel injection strategies were 41.50%. The main-post diesel injection strategy slightly decreased IFE of NDDF (i.e., 40.35%). However, an optimized combustion phasing and pre-main-post injection strategy made it possible to achieve similar or higher IFE than single injection strategy. Moreover, the pre-main-post diesel injection strategy significantly decreased unburned methane emissions. The lowest measured unburned methane emissions when using pre-main-post diesel injection was 0.37 g/kW.h, which was lower than that of single injection (0.80 g/kW.h). Compared to single diesel injection, optimized combustion phasing along with pre-main-post injection strategy reduced GHG and NOx emissions by 10% and 47%, respectively.

Study on Combustion Processes of a Premixed Charge Compression Ignition (PCCI) Engine Fueled with DME/Diesel

A dimethyl ether (DME) pre-mixing system was installed on a 2105 diesel engine for realizing pre-mixed charge compression ignition combustion mode. Combustion processes of a PCCI engine fueled with DME/diesel under various DME pre-mixing ratios were investigated in this paper. The results showed that the heat release process showed three stages with port induction of DME. As the DME pre-mixing ratio (PR) increased, the peak value of cylinder temperature and pressure raised and the corresponding crank angles advanced. The start of combustion (SOC) moved forward obviously and the duration of combustion extended; the peak value of the pressure rise rate reduced first and then raised. The results in this paper provided a reference for the combustion process optimization of DME/diesel PCCI engine.

Effects of n-butanol/calophyllum inophyllum biodiesel blend injection on the combustion characteristics of reactivity controlled compression ignition engine

The present experiment work implements the reactivity controlled compression ignition (RCCI) technique in analysing the combustion, performance, and emissions (regulated and unregulated) characteristics of diesel engine. A high reactivity calophyllum inophyllum biodiesel blend (B20) is directly injected inside the cylinder and a low reactivity n-butanol fuel is injected in three different ratios (10%, 20% and 30% by vol. basis) into the inlet manifold section using the electronic control unit. This study reveals that the brake thermal efficiency increased by 4.32%, oxides of nitrogen, smoke, acetaldehyde, benzaldehyde, hexanaldehyde, are reduced 19.31%, 8.82%, 12.19%, 11.71% and 37.02%, respectively compared to diesel at full load condition. The carbon monoxide, hydrocarbons, formaldehyde, crotanaldehyde are increased by 15.23%, 20.87%, 15%, and 13.23% compared with neat diesel fuel. The cylinder pressure and heat release rate are increased by 18%, 29.15% with n-butanol 30% injection due to the advanced start of combustion, high cylinder temperature, and better mixture formation. [Received: September 19, 2019; Accepted: June 26, 2020]

Комплексная методика исследования степени термического поражения стальных элементов транспортных средств с помощью полевых методов

Introduction. Every year, the number of registered motor vehicles in Russia increases, with an increase of 30 % over the past 10 years. The desire to extend the service life of existing vehicles leads to an increase in breakdowns that lead to fire. The task of identifying places where there was an emergency situation that led to a fire is difficult, especially in the case of a complete burnout of the fuel load of the car. Goals and objectives. The purpose of the work is to create a methodology by which it is possible to conduct studies of cold-formed steel products of the vehicle body to determine the zone of the greatest thermal damage. Each method determines one of the characteristics that changes when the steel is exposed to high temperatures. The main task of the work is to test the possibility of applying these methods in a certain sequence to determine the zone that has undergone more annealing. Research methods. The complex method includes induction thickness measurement, which allows measuring the thickness of a layer of high-temperature oxide; a method for measuring the coercive force or demagnetization currents, as well as a method for measuring microhardness. The latter method will determine the decrease in the hardness of the vehicle body after exposure to high temperatures. Results and its discussion. The obtained data on the degree of thermal damage to cold-deformed steel products of the car body by three independent field methods will increase the reliability of the combustion start zone, which in turn will determine the search zone for the cause of ignition. Conclusion. Determining the specific cause of the fire during the maintenance, repair and operation of vehicles will allow you to exclude similar emergency modes in the future. The introduction of a comprehensive method for investigating the condition of an object after a fire will significantly increase the level of reliability of the results obtained when searching for a breakdown that led to a fire. Keywords: fire source, car body, thermal changes, field methods, complex technique, magnetic properties, scale thickness, microhardness

Simulation analysis of the effects of methanol-polyoxymethylene dimethyl ethers blends on combustion and emissions of a PCCI engine

The effects of methanol/polyoxymethylene dimethyl ethers (PODE) mixture with different blending ratios on premixed charge compression ignition (PCCI) combustion and emission performance have been researched through the anlysis of CFD software CONVERGE. Premixed combustion is achieved by a single early injection of fuel into the cylinder. The results show that the combustion start point delays and the peak pressure decreases with the increase of methanol blend ratio. The effects of injection timing on the combustion and emission characteristics of PCCI were studied by using a mixture of the same proportion of methanol. The results show that the advance of injection time leads to more homogeneous mixture and higher peak heat release. But too early injection reduces the temperature in the cylinder and makes the combustion worse, resulting in the increase of HC, soot and CO emissions. NOx emissions decrease with the advance of the injection time.

Optimization of Injection Pressure and Injection Timing on Fuel Sprays, Engine Performances and Emissions on a Developed DI 20C Biodiesel Engine Prototype

Biodiesel, as a renewable fuel that has the potential to replace diesel fossil fuels. With properties in the form of viscosity, density, and surface tension, which are higher than diesel fossil fuel, biodiesel produces poor spray characteristics, and also the high cetane number and oxygen content so that the ignition delay is shorter causes the start of combustion will shift more forward, therefore need to improve injection parameters including injection pressure and timing. The aim of this research is to get the optimal injection parameter optimization so as to improve engine performances and emissions. The method used is to increase the fuel injection pressure from 200 to 230 kg/cm2 and the injection timings were retarded from 22° to 16° BTDC. The results show that increasing injection pressure can improve spray characteristics as indicated by shorter penetration and smaller spray diameter of 30% and 9.8%, respectively and increase in spray spread angle of 21.9%. Then the optimization of engine performances and emissions, obtained at an injection pressure of 230 kg/cm2 and injection timing of 16° BTDC with an increase of power and thermal efficiency of 3.9% and 13.9%, respectively and reduction in smoke emissions of 45.2% at high load.

Effects of ethane addition on diesel-methane dual-fuel combustion in a heavy-duty engine

The present study is a continuation of the previous work by Ahmad et al. (2020), in which ethane (C2H6) enriched diesel-methane (CH4) dual-fuel (DF) combustion was experimentally investigated in a single-cylinder heavy-duty engine. Here, the experiments of ethane enriched DF combustion are carried out with new details together with supporting zero-dimensional (0D) and one-dimensional (1D) chemical kinetics simulations. Three port-fuel injected (PFI) gaseous blends of pure methane with varying ethane concentrations of 0%, 10%, and 20% are used as the main fuels. The PFI gaseous blend provides 97% of the total-fuel energy (TFE), which is ignited by a small 3% (TFE based) pilot diesel. Experiments are performed under lean condition (∅gas = 0.52) for two engine speeds while keeping the TFE and other operating conditions constant. Calculated results from 0D and 1D simulations under engine relevant conditions including theoretical combustion mode analysis (β-curve) are used to deepen the phenomenological understanding of the experimental results. The results reveal that adding ethane into pure methane has minor effects on the pilot-diesel ignition timing. However, ethane addition greatly enhances the ignitability of methane after the start of combustion. Ethane enriched gaseous blends yield higher thermal efficiency and reduce combustion duration compared to pure methane. According to combustion mode analysis, ethane tendency to promote spontaneous autoignition may be one of the reasons for improving overall combustion performance. It is observed that ethane enriched gaseous blends produce lower unburned methane (UB-CH4) and unburned hydrocarbons (THC) accompanied with higher nitrogen oxides (NOx) because of the higher combustion efficiency. Furthermore, ethane addition considerably helps to reduce cycle-to-cycle variations under lean conditions compared to pure methane.

Combustion phase of a diesel/natural gas dual fuel engine under various pilot diesel injection timings

Although the brake thermal efficiency and exhaust emissions performance of the engine have been improved significantly in recent years, these issues are still not fully-resolved. Natural gas (NG) engine has been widely concerned because of its extensive resources and relatively clean. To better understand the effect of the pilot diesel injection timing on the combustion phases of the pilot diesel and the natural gas, a detailed study was conducted by experiment and numerical simulation. A 6-cylinder turbocharged intercooler diesel/natural gas dual fuel heavy-duty engine was used in this study, and the pilot diesel injection timing was controlled over a very wide range at a constant engine speed of 1335 r/min. The results show that the injection timing has an obvious effect on the engine combustion process including combustion phases of the pilot diesel and the natural gas, and which decide the engine thermal efficiency and exhaust emissions level. The chemical reaction of diesel and natural gas before combustion start at the same time, however, the combustion duration of natural gas lags behind that of diesel. In addition, during the combustion overlap period, the in-cylinder combustion is good and the working ability is strong. To advance the pilot diesel injection timing from 5 °CA BTDC to 35 °CA BTDC, the chemical ignition delay of diesel shows a lengthening trend, and the combustion duration shows a shortened trend. With advancing the pilot diesel injection, the natural gas combustion duration shows a shortened trend, and the shortest is near to 16.5 °CA. There is a clear correspondence between the lengths of combustion period of two fuels. Either the combustion duration or the combustion overlap period shows a shortened trend, but the ratio of the combustion overlap period to the combustion duration is increasing with advancing the pilot diesel injection. The shortest combustion duration corresponds to the lower brake specific energy consumption and emissions.

Numerical Investigation of the Characteristics of the In-Cylinder Air Flow in a Compression-Ignition Engine for the Application of Emulsified Biofuels

This paper presents a numerical analysis of the application of emulsified biofuel (EB) to diesel engines. The study performs a numerical study of three different guide vane designs (GVD) that are incorporated with a shallow depth re-entrance combustion chamber (SCC) piston. The GVD variables were used in three GVD models with different vane heights, that is, 0.2, 0.4 and 0.6 times the radius of the intake runner (R) and these were named 0.20R, 0.40R and 0.60R. The SCC piston and GVD model were designed using SolidWorks 2017, while ANSYS Fluent version 15 was used to perform cold flow engine 3D analysis. The results of the numerical study showed that 0.60R is the optimum guide vane height, as the turbulence kinetic energy (TKE), swirl ratio (Rs), tumble ratio (RT) and cross tumble ratio (RCT) in the fuel injection region improved from the crank angle before the start of injection (SOI) and start of combustion (SOC). This is essential to break up the heavier-fuel molecules of EB so that they mix with the surrounding air, which eventually improves the engine performance.

Three-dimensional numerical simulations on the effect of ignition timing on combustion characteristics, nitrogen oxides emissions, and energy loss of a hydrogen fuelled opposed rotary piston engine over wide open throttle conditions

Opposed rotary piston (ORP) engines have advantages of high power density, few moving parts, and smooth operations, which makes ORP engines as potential power sources for hybrid vehicles and range extended electric vehicles. Ignition timing significantly affects the performance of spark ignition engines including fuel economy and emission factors. In this paper, the effect of ignition timing on the engine performance was investigated using a three-dimensional numerical simulation method. The results indicated that crank angle corresponding to the peak in-cylinder pressure over the ignition timing of −8.2° crank angle (CA) was advanced compared with other cases having earlier ignition timing; however, the crank angle of peak heat release rates were retarded. Start of combustion was delayed by retarding the ignition timing and increasing engine speed; combustion duration over the ignition timing of −18.9° CA ~ −11.1° CA changed slightly for individual engine speed. Indicated specific fuel consumption (ISFC), being hardly dependent on the ignition timing, was less than 74 g/(kW·h) over the ignition timing of −17.3° CA ~ −11.1° CA, where indicated thermal efficiency was approximately 41%, 39% and 35% for 1000 RPM, 3000 RPM and 5000 RPM respectively. When ignition timing was later than −11.1° CA, ISFC and indicated thermal efficiency were deteriorated seriously. Nitrogen oxides (NOx) emission factors increased with engine speed over early ignition timing; however, they were inverse for late ignition cases. Higher engine speed and retarded ignition timing led to higher percentage of exhaust energy in fuel chemical energy.

An experimental study of uncertainty considerations associated with predicting auto-ignition timing using the Livengood-Wu integral method

The application of the Livengood-Wu (LW) integral method as a tool to estimate knock onset in spark ignited (SI) engines and combustion phasing in advanced compression ignition (ACI) engines has been demonstrated through simulations several times. In this study, the effect of uncertainties associated with parameters required for the LW integral method, when used as a tool for model based control of ignition timing in an ACI engine, were experimentally studied using five full boiling range gasoline fuels. As a first step, the method was applied to experimental data from a rapid compression machine and it was found that the ability of the LW integral method to predict ignition timing was very sensitive to the performance of the chemical kinetic model of each fuel. The method was subsequently applied to experimental data from a single-cylinder gasoline engine with simple approximations for the LW integral input parameters, and it was found that the predicted time of ignition was significantly different from the actual start of combustion. Systematic evaluation of various parametric uncertainties conducted thereafter showed that the uncertainty in cylinder charge temperature has the greatest influence. Improved methods of estimating cylinder charge temperature are proposed to account for the previously determined corrections, to enable the use of the LW integral method for model based control of ignition timing.

Resonant Combustion Start Considering Potential Energy of Free-Piston Engine Generator

Free-piston engine generators without a crank mechanism are expected to be used in series hybrid vehicles because of their lower losses. The series hybrid system requires a low starting thrust because the engine frequently starts depending on the battery state. This study clarifies the effectiveness of the constant thrust resonance starting method that utilizes the compression pressure of the engine and the spring thrust. The piston must pass the combustion starting point with a predetermined speed to start combustion. Herein, we present a thrust setting method that uses the energy state diagram to optimize the velocity at the combustion start point. A simulation is performed assuming output when mounted on a vehicle. Consequently, the simulation results show that the maximum thrust can be reduced by more than 90% compared to that without resonance. Moreover, the speed at the combustion start point is in agreement with the value obtained using an energy state diagram. An impulse-like combustion pressure is generated in 180 ms, and combustion can be started using resonance, as shown in an experiment using a small-output engine and linear motor. The effectiveness of the constant thrust resonance starting method was confirmed.

Experimental and Numerical Validation of In-Cylinder Combustion Analysis of DI Diesel Engine

The major factors affecting the process of combustion in a single cylinder diesel engine is in-cylinder fluid flow characteristics. Better fuel-air mixing and combustion rates in diesel engine are primarily enhanced by the fluid flow. The fluid flow prior to combustion process in DI diesel engines travel through induction process and further gets improvised during the compression process. Therefore, it is compulsory to understand the fluid flow motion inside the cylinder in designing the different bowl-in-piston geometries with the most appropriate operating and emission characteristics. A better spatial distribution is required for the injected fuel throughout the entire space of combustion geometry in DI diesel engine, to obtain a better combustion with lesser emission. In order to effectively make use of gas flows it is mandatory to match the piston bowl geometry with fuel spray characteristics. For obtaining better combustion, matching of combustion chamber geometry, fuel injection and gas flows plays prominent role. But it is evident that piston bowl geometry plays a significant role on flow of compressed air when piston moves from BDC to TDC i.e., before the start of combustion, resulting in proper mixing, better vaporization and atomization of fluid particles. When compared with other combustion chambers, Off-set bowl in the absence of central projection with sharp edges provide higher swirl number. Higher these whirl number lesser will be the soot emission at the expense of higher NOx level.

Cold-start NOx emissions: Diesel and waste lubricating oil as a fuel additive

NOx emissions from diesel engines are a concern from both environmental and health perspectives. Recently this attention has targeted cold-start emissions highlighting that emission after-treatment systems are not effective in this period. Using a 6-cylinder, turbocharged, common-rail diesel engine, the current research investigates NOx emissions during cold-start using different engine performance parameters. In addition, it studies the influence of waste lubricating oil on NOx emissions introducing it as a fuel additive (1 and 5% by volume). To interpret the NOx formation, this study evaluates different parameters: exhaust gas temperature, engine oil temperature, engine coolant temperature, start of injection/combustion, in-cylinder pressure, heat release rate, maximum in-cylinder pressure and maximum rate of pressure rise. This study clarified how cold-start NOx increases as the engine is warming up while in general cold-start NOx is higher than hot-start. Results showed that in comparison with warmed up condition, during cold-start NOx, maximum in-cylinder pressure and maximum rate of pressure rise were higher; while start of injection, start of combustion and ignition delay were lower. During cold-start increased engine temperature was associated with decreasing maximum rate of pressure rise and peak apparent heat release rate. During cold-start NOx increased with temperature and it dropped sharply due to the delayed start of injection. This study also showed that using waste lubricating oil decreased NOx and maximum rate of pressure rise; and increased maximum in-cylinder pressure. NOx had a direct correlation with the maximum rate of pressure rise; and an inverse correlation with the maximum in-cylinder pressure.