Agricultural & municipal waste and wood residues can be easily converted to biogas or producer gas and used for producing heat and power. The main problem with these fuels is their low energy content. This is due to the presence of certain non-combustible gases like CO 2 and N 2 in these fuels. The use of these gases in SI engines is associated with problems like unstable operation and high levels of HC and CO emissions. Gaseous fuel can be easily used with good efficiencies and low emissions in diesel engines running in the dual-fuel mode. In dual-fuel engines, these gaseous fuels are inducted along with air and ignited after compression by a small spray of diesel called the pilot. The presence of these gases alters the thermodynamic properties of the intake charge and significantly influence the ignition delay of the pilot diesel fuel and hence the performance of the engine. The aim of this paper is to modify an existing correlation for ignition delay in a dual-fuel engine to incorporate the effects of the gaseous fuel concentration and composition on the polytropic index. An ignition delay correlation of a biogas dual-fuel engine was modified so that it can be used with any primary fuel. The polytropic index was assumed to be a function of the ratio of specific heats. Further, the effect of injection timing on ignition delay was included. The adapted model was introduced in a simulation program and the results of ignition delay were compared with those given in the literature for a dual-fuel engine. In addition, the correlation was used to predict the ignition delay of the pilot fuel when biogas, LPG, natural gas and producer gas were treated as primary fuels. The results obtained with the new correlation have been compared with experimental values from a LPG-diesel dual fuel engine. The comparison was also made for a biogas dual fuel engine. Errors less than 10% were obtained for both of the fuels between the experimental measurements and simulation results.

Effect of fuel injection timing relative to ignition timing on natural gas direct-injection combustion was studied by using a rapid compression machine. The ignition timing was fixed at 80 ms from the compression start. When the injection timing was relatively earlier (injection start at 60 ms), the heat release pattern showed slower burn in the initial stage and faster burn in the late stage, which is similar to that of flame propagation of a premixed gas. In contrast to this, when the injection timing was relatively later (injection start at 75 ms), the heat release rate showed faster burn in the initial stage and slower burn in the late stage, which is similar to that of diesel combustion. The shortest duration was realized at the injection end timing of 80 ms (the same timing as the ignition timing) over the wide range of equivalence ratio. The degree of charge stratification and the intensity of turbulence generated by the fuel jet is considered to cause these behaviors. Earlier injection leads to longer duration of the initial combustion, whereas the later injection does longer duration of the late combustion. Earlier injection showed relatively lower CO emission while later injection produces relatively lower NOx emission. It was suggested that earlier injection leads to lower mixture stratification combustion and later injection leads to higher mixture stratification combustion. Combustion efficiency maintained high value over the wide range of equivalence ratio.

CFD simulations need a certain number of parameters to calibrate both empirical and analytical models. The present investigation aims at identifying the effects of these parameters on the numerical prediction of a modified version of Kiva 3V code, which includes the use of the RNG k-ε model for turbulence, the gas/wall convective heat transfer model proposed by Han, Kelvin-Helmholtz Rayleigh-Taylor spray injection and breakup models. Ignition delay was modeled with the Shell model, whereas the laminar-turbulent characteristic time model was used for combustion. Soot formation and oxidation were calculated using Hiroyasu and Nagle and Strickland-Constable models, respectively. NO x was predicted by using the extended Zel’dovich mechanism. This study was carried out for a common-rail direct injection, small-bore Diesel engine, including the investigation of both numerical and physical parameters. Numerical parameters are intended to be variables related to breakup, turbulence, and combustion models that are adjusted according to grid resolution, engine and injection system geometry, and operating conditions. In particular, the effect of laminar and turbulent time scales, characteristic breakup length and time scales, initial turbulence kinetic energy density, initial swirl velocity profile, on engine emissions was analyzed. The investigated physical parameters were initial swirl ratio, air water content, Schmidt number for mass diffusion. All simulations were performed by changing one of the above parameters at each run and keeping approximately the same pressure and heat release rate curves. Results show that similar pressure vs. crank angle curves can be obtained with different values of these parameters but they lead to very different values of predicted emissions levels. In particular, changes of laminar and turbulent characteristic time resulted in a strong influence on NO x emissions but their effects on soot levels were minor. Mass diffusion characteristics (e.g. Schmidt number) were found to strongly affect both soot and NO x emissions. Spray parameters were found mainly to affect soot formation. Furthermore, NO x and soot emissions showed a dependence on swirl ratio and velocity profile.

In this paper, some basic properties of homogeneous charge compression ignition operation are investigated. The HCCI operating range for a CFR engine was determined with n-butane as fuel. The minimum and maximum load was determined using criteria of covariance of indicated mean effective pressure and the derivative of in-cylinder pressure respectively. Exhaust emissions, particularly hydrocarbons, were measured using a Fourier transform infrared spectrometer. The concentration of intermediate hydrocarbon species rapidly decreased as the magnitude of the heat release increased. Hydrocarbon emission at the maximum HCCI load mainly consists of the fuel itself, which is probably emitted from colder areas in the combustion chamber. The relation between IMEPCOV and ISFC is discussed.

This study investigated the effect of combustion chamber geometry and initial mixture distribution on combustion process in a direct-injection diesel engine by means of experiment and CFD calculation. The high squish combustion chamber with squish lip could produce simultaneous reduction of NOx and particulate emissions with retarded injection timing in the real engine experiment. According to the CFD computation, the high squish combustion chamber with central pip is effective to continue combustion under the squish lip until the end of combustion and the combustion region forms rich and high turbulence atmosphere, which reduces NOx emissions. This chamber can also reduce initial burning because combustion continues under the squish lip. The CFD computation is also carried out in order to investigate the effect of initial mixture distribution on combustion process. The results suggest that mixture distribution affects the history of heat release rate. When fuel is distributed in the bottom or wide region in the combustion chamber, burned gas tends to spread to the cavity center and initial heat release rate becomes high. On the contrary, the high squish combustion chamber with central pip produces lower initial heat release rate because combustion with local rich condition continues long under the squish lip. Diffusion burning is promoted by high swirl motion in this chamber with keeping lower initial heat release rate.

An experimental investigation has been carried out to study the effects of using water / diesel emulsion fuel in an indirect injection diesel engine on the heat flux crossing liner and cylinder head, thermal loading and metal temperature distribution. A single cylinder precombustion chamber diesel engine has been used in the present work. The engine was instrumented for performance, metal temperature and heat flux measurements. The pure gas oil fuel and different ratios of water / diesel emulsion were used and their effects on the heat flux level and the injector tip temperature are studied. Two correlation were found for the heat flux crossing the liner and the cylinder head at various water / diesel emulsion ratios, fuelling rate and thermocouple probe locations. It was found that the addition of water to diesel fuel, to control the nitrogen oxides emissions, has great influence on reducing die heat flux, the metal temperatures and thermal loading of combustion chamber components.

This paper describes that an analysis of oil film thickness on a piston ring of diesel engine. The oil film thickness has been performed by using Reynolds equation and unsteady, two-dimensional (2-D) energy equation with a heat generated from viscous dissipation. The temperature distribution in the oil film is calculated by using the energy equation and the mean oil film temperature is computed. Then the viscosity of oil film is estimated by using the mean oil film temperature. The effect of oil film temperature on the oil film thickness of a piston ring was examined. This model has been verified with published experimental results. Moreover, the heat flow at ring and liner surfaces was examined. As a result, the oil film thickness could be calculated by using the viscosity estimated from the mean oil film temperature and the calculated value is agreement with the measured values.

A combined thermodynamic power system is described that uses a two-phase fluid (air and water) to form the basis of a cycle that employs the isothermal compression of the working fluid to improve the overall efficiency. The compressor and the expander described in the system utilize sliding-blade rotary devices that together make up an air-heat engine that operates on a modified Brayton cycle. Key to this device is the utilization of an isothermal compression of the air and the efficient use of waste heat in a regenerative process to achieve high thermal efficiency and reduce environmentally damaging emissions. In addition, a special pre-chamber/vortex combustion chamber allows for the introduction of heat in an environmentally friendly manner.

The hot tests on a prototype waste heat thermal recuperation system attached to a heavy-duty diesel engine and used with an inert gas as the cycle organic refrigerant described. TER is a system attached to the engine that uses the waste heat in the hot coolant and can lead to an efficiency improvement of 2 to 4% with correspondingly lower emissions. The heat balance, pressure losses, energy available for recuperation and other pertinent data are described and discussed. The equipment proved to be rugged. High-pressure losses in the system were reduced and the heat losses improved. The TER55 refrigerant was easier to handle and could serve as a reasonable substitute for Butane: it is inert, non-CFC based and operates at similar pressures.

There has been an extensive worldwide search for alternate fuels that fit with the existing infrastructure and would thus displace fossil-based resources. In metabolic engineering work at Argonne National Laboratory, strains of fuel have been designed that can be produced in large quantities by photosynthetic bacteria, eventually producing a heavy alcohol called phytol (C 20 H 40 O). Phytol’s physical and chemical properties (cetane number, heat of combustion, heat of vaporization, density, surface tension, vapor pressure, etc.) correspond in magnitude to those of diesel fuel, suggesting that phytol might be a good blending agent in compression ignition (CI) engine applications. The main reason for this study was to investigate the feasibility of using phytol as a blending agent with diesel; this was done by comparing the performance and emission characteristics of different blends of phytol (5%, 10%, 20% by volume) with diesel. The experimental research was performed on a single-cylinder engine under conventional operating conditions. Since phytol’s viscosity is much higher than that of diesel, higher-injection-pressure cases were investigated to ensure the delivery of fuel into the combustion chamber was sufficient. The influence of the fuel’s chemical composition on performance and emission characteristics was captured by doing an injection timing sweep. Combustion characteristics as shown in the cylinder pressure trace were comparable for the diesel and all the blends of phytol at each of the injection timings. The 5% and 10% blends show lower CO and similar NO x values. However, the 20% blend shows higher NO x and CO emissions, indicating that the chemical and physical properties have been altered substantially at this higher percentage. The combustion event was depicted by performing high-speed natural luminosity imaging using endoscopy. This revealed that the higher in-cylinder temperatures for the 20% blend are the cause for its higher NO x emissions. In addition, three-dimensional simulations of transient, turbulent nozzle flow were performed to compare the injection and cavitation characteristics of phytol and its blends. Specifically, area and discharge coefficients and mass flow rates of diesel and phytol blends were compared under corresponding engine operating conditions. The conclusion is that phytol may be a suitable blending agent with diesel fuel for CI applications.

One of the key conjunctions in the IC engine is that made by the top compression ring to the cylinder liner. Although the compression ring has seen considerable improvements since its introduction into steam engines by John Ramsbottom in the 1850s, its multiple and often contradictory functions still remain a challenge today. The primary aim has always been to seal the combustion chamber and guard against leakage of combustion gasses. The ring is also required to conduct some of the generated heat away. These requirements call for good ring-bore conformance, but often at the expense of increased friction. A simplified inter-ring gas flow model, as well as the measured chamber pressure using a Kistler pressure transducer is carried out under motored conditions to obtain the net gas pressure acting behind the ring. This and the elastic pressure as the result of ring restoring tension force in fitment constitute the contact load, which is usually carried by a mixed-hydrodynamic regime of lubrication. The conjunction pressures are treated as a combination of hydrodynamic generated pressures and asperity-pair interactions. The former is obtained by solution of two dimensional Reynolds equation, whilst the latter is determined assuming a Gaussian distribution of asperities on the counterfaces. Surface topography of the bounding solids; the compression ring and the liner are measured and used as appropriate statistical functions in the Greenwood and Tripp model. Using an analytical flow model, pressure acting behind the ring (on the inner periphery of the ring) is obtained, leading to the calculation of ring-bore friction. A floating liner is used to measure friction of piston and ringpack in situ . The characteristic of the predicted variations are compared with the measured data. However, a quantitative comparison is not possible as the measured data corresponds to all the conjunctions of piston system, including the oil control rings as well as the piston skirt. The results show that variation of gas force behind the ring significantly changes the ring-bore contact, thus friction and the nature of interactions.

A first-order lumped-parameter model for the prediction of thermal behavior of a single-cylinder gasoline engine for Hybrid Electric Vehicles (HEVs) has been implemented. The model is coupled with a zero-dimension in-cylinder model that evaluates the working cycle of the engine according to the actual operating conditions and calculates the temperature of the exhaust gases, the overall efficiency of the engine and the exhaust gases flow rate. The model takes into account the possibility of using exhaust gas heat recirculation in order to enhance engine warm-up during cold start which improves its efficiency. The supervisory strategy takes into account not only predicted speed and ambient and road conditions along a future time window but also actual battery state of the charge and engine temperature to select the optimal power split between the ICE-generator group and the batteries. The proposed model represents an improvement with respect to a previous investigation of the authors where the temperature of the engine were assumed to increase/decrease of on Celsius degree in each seconds according to the state of the engine (ON/OFF).

The regime of lubrication changes in a transient manner in many load bearing conjunctions. This is particularly true of any conjunction which is subjected to changes in contact kinematics as the result of stop-start or motion reversals and loading. One such conjunction in the IC engine is the piston-bore contact. A repercussion of these transient events under otherwise perceived steady operating condition is the underlying changes in the mechanisms giving rise to engine efficiency, such as parasitic losses, mainly due to friction. Understanding the nature of these losses is the prelude to any form of palliation. A single cylinder motocross motorbike engine’s cylinder barrel is redesigned to accept wet liners with various incorporated instrumentation. The paper describes one such barrel which incorporates an instrumented floating liner for the purpose of measurement of in-cylinder friction. The principle and design of the floating liner is described. A series of tests are carried out in order to ensure the operational integrity and repeatability of the device. The basic test includes motorised running of the engine without the cylinder head installed. This renders simplified motion of the liner, subject to resistance by friction only. In a sense, under this type of motion, the liner should undergo a form of simple harmonic motion, which is verified using a number of suitably positioned accelerometers. Some more representative tests are reported under motorised conditions with the cylinder head installed. Thus, the effect of chamber pressure is introduced. However, with no combustion pressure, heat output and resulting side forces, a better understanding of tribological conditions is accrued owing to the reduced physical interactions. The results show the dominance of a mixed regime of lubrication at the dead centre reversals.

A predictive zero-dimensional low-throughput combustion model that was previously developed by the authors has been refined and applied to a EURO V diesel automotive engine. The model is capable of simulating, in real time, the time-histories of the HRR (Heat Release Rate), in-cylinder pressure, in-cylinder temperatures and NO x (nitrogen oxides) concentrations, on the basis of a few quantities estimated by the ECU (Engine Control Unit), such as the injection parameters, the trapped air mass, the intake manifold pressure and temperature. It has been developed for model-based feedforward control purposes in DI (Direct Injection) diesel engines featuring an advanced combustion system or new combustion-mode concepts, such as LTC/PCCI (Low Temperature Combustion/Premixed Charge Compression Ignition) engines. In the present work, the model has been assessed in detail by analyzing a wide set of experimental engine data that were acquired during the engine calibration phase. The experimental data set has been defined according to the DoE (Design of Experiment) methodology currently used for engine calibration purposes, and applied to six ‘key-points’ that are representative of engine working operations during an NEDC (New European Driving Cycle) for a D-class passenger car. Different injection strategies (pilot-main, double pilot-main; pilot-main-after; double pilot-main-after) have been considered for each key point, and all the main engine operating parameters (rail pressure, injected quantities, boost level, intake temperature, EGR rate,…) have been included in the DoE variation list. Therefore, about 1000 steady-state engine operating conditions have been investigated. In addition, several NEDC driving cycles have been realized with the engine installed on a dynamic test rig, and the combustion parameters and emission levels have continuously been measured during the transient operations. The model has been applied to all the investigated conditions. It has shown excellent accuracy in estimating the values of the main combustion parameters, and a good matching between the calculated and predicted NO x concentrations was found, for both steady-state and transient operations.

Over a significant period of time, efforts have been made towards a valid and accurate estimation of DI diesel engine NO x emissions. Considering the fact that experiments have a high cost in both time and money, modelling approaches have been developed in an effort to overcome these issues. It is well known that accuracy in the prediction of NO x emissions lies specifically on the accurate estimation of local temperature and O 2 histories inside the combustion chamber that govern NO x formation, fulfilled by an accurate estimation of the combustion mechanism. To account for the actual effect of parameters that control NO x formation and overcome inefficiencies introduced from existing purely empirical models or artificial neural networks, valid only on the combustion systems for which they were developed [1], an alternative solution is the introduction of physically based semi-empirical models. Towards this direction, in the present work is presented and evaluated a new modelling approach, based on the combustion rate obtained from the measured cylinder pressure trace using Heat Release Rate Analysis. The model used is a semi-empirical two-zone one which makes use of the estimated elementary fuel mass burnt at each crank angle interval. The combustion process is considered to be adiabatic, while chemical dissociation is also considered. With this approach, temperature distribution throughout the combustion chamber is considered for, together with its evolution during the engine cycle. In addition, O 2 availability is also considered for through the calculated charge composition. The result is an extremely fast computational model, combining the advantages of both empirical and physically based ones. In the present work is given a detailed validation of the model, from its application on two different types of diesel engines: a heavy-duty DI diesel engine and a light-duty DI diesel engine with pilot fuel injection. A significant number of cases where tested for both engine configurations, considering different operation points and variation of operating parameters, such as rail pressure and EGR. The twelve points of the European Stationary Cycle (ESC) were covered for the case of the heavy duty DI diesel engine, whilst for the light-duty DI engine a total number of forty-six operating points was studied. For both engine configurations the model reveals a very good predictive ability, considering for the effect of all operating parameters examined on NO x emissions. However, there is potential for improvement and development on its physical base for even more accurate predictions. The merits of good accuracy in prediction trends with varying engine operating parameters — even without calibration — and low computational time establish a potential for model use in engine development, optimization studies and model based control applications.

Advanced premixed compression ignition (CI) combustion using fumigation has been shown to yield significant improvements in indicated efficiency over traditional diesel combustion strategies while simultaneously reducing engine-out soot and NO X emissions. To better interpret these findings, a breakdown of the ways in which actual performance deviates from ideal engine cycles is helpful. Non-ideal combustion phasing is one cause of such deviations. In this paper, the centroid of the calculated apparent heat release rate is used to estimate an adjusted maximum possible thermal efficiency based on constant volume combustion using an effective compression ratio concept. Using these metrics, experimental engine data are evaluated from a single cylinder direct-injection diesel engine operating in premixed CI mode enabled by gasoline fumigation and a diesel pilot injection. Indicated gross cycle efficiency was found to be higher for premixed fumigation compared with a conventional diesel condition at the same load. A key finding of the work is that the peak indicated cycle efficiency for fumigated premixed CI combustion occurs with combustion phased very close to TDC. Shorter heat release duration and lower heat losses from the cylinder are thought to be the cause of differences in cycle efficiency between conventional combustion and premixed CI fumigation modes.

This study investigates how injection timing affects combustion, NO x , PM mass and composition from a 2-stroke turbocharged locomotive diesel engine fitted with an early-development Tier 0+ emissions kit. The objective of the work is to gain insight into how injection timing affects combustion and emissions in this family of engines, modified to meet the newly implemented Tier 0+ emissions requirements, and to identify areas of potential future emissions reduction. For a range of injection timings at a medium load (notch 5) operating condition, the majority of PM mass is comprised of insolubles (81–89%), while the soluble component of PM (SOF) accounts for a smaller fraction (11–19%) of total PM mass. The SOF is 66–80% oil-like C 22 –C 30+ hydrocarbons, with the remainder being fuel-like C 9 –C 21 hydrocarbons. A heat release analysis is used to elucidate how injection timing affects combustion by calculating mass fraction burn curves. It is observed that retarding injection timing retards combustion phasing, decreases peak cylinder pressure and temperature, and increases expansion pressure and temperature. Results show that insolubles and fuel-like hydrocarbons increase and oil-like hydrocarbons decrease with later injection timing. Analysis suggests that insolubles and fuel-like HC increase due to lower peak combustion temperature, while oil-like HC, which are distributed more widely throughout the cylinder, decrease due to higher expansion temperatures. The net result is that total PM mass increases with retarded combustion phasing, mostly due to increased insolubles. Considering the high fraction of insoluble PM (81–89%) at all injection timings tested at notch 5, steps taken to reduce PM elemental carbon should be the most effective path for future reductions in PM emissions. Further reductions in oil consumption may also reduce PM, but to a smaller extent.

This work deals with the analysis of the performance and emissions of ethanol HCCI/PSCCI engines by means of a Dynamic Adaptive Chemistry (DAC) technique. The implementation of such a technique provides a reduction of the computational cost of the simulations without compromising the reliability of the results. Very accurate results, in terms of pressure and heat release rate profiles and CO, CO 2 and UHC emissions, are obtained with ethanol as the only species for the DRGEP graph search both with the charge uniformly distributed in the combustion chamber and by directly injecting liquid fuel in the same chamber. The global speed up of DAC simulations is twice with respect to a full mechanism which consists of 57 species and 288 reactions and a further increase is expected when DAC is compared to very detailed kinetics.

Lean large-bore natural gas engines are usually equipped with gas-scavenged prechambers. After ignition and during combustion in the prechamber hot reacting jets penetrate the main chamber and provide much higher ignition energies than electric spark plugs. Although prechambers stabilize combustion, limitations of the concept are observed at very lean main chamber mixtures and large cylinder diameters, which appear as cycle-to-cycle variations of heat release and pressure. At the Thermodynamics Institute of the Technical University of Munich cycle-to-cycle variations are investigated in an unique periodically chargeable high pressure combustion cell with full optical access to the entire main chamber. Recently, the influence of the ignition timing, the amount of scavenge-gas of the prechamber and the cross section of the prechamber exit orifices on cycle-to-cycle variations have been studied. From the pressure traces characteristic parameters of the combustion process like the ignition probability, the ignition delay and the rate of the pressure rise have been derived. By analysing the emission of OH*-chemiluminescence in terms of reacting area and light emission and on the basis of numerical simulations information on the source of cycle-to-cycle variations is obtained. Finally it is shown that cycle-to-cycle variations can be reduced remarkably by appropriate selection and combination of prechamber geometry and operating parameters.

Reciprocating engines are still frequently used in aviation especially in applications such as recreation planes, taxi-planes, fire extinguishing aircraft and generally applications that do not require a high power density. For such applications they have a significant advantage against turbine engines as far as purchase and maintenance cost is concerned. The proper and efficient operation of these engines in aviation applications is critical and therefore techniques that are used to determine engine condition and to detect potential faults are extremely important. The performance of these engines depends strongly on the condition of the ignition system and the quality of the supplied mixture. For this reason in the present work it is examined the effect of mixture AFR on the combustion mechanism and engine performance using an existing diagnostic methodology for spark ignited engines developed by the present research group. The investigation is conducted on a radial, spark-ignited reciprocating engine used on the CL-215 fire extinguishing aircraft. The diagnostic technique is used to investigate the effect of AFR on the main combustion and performance characteristics of the engine and specifically brake power output, rate of heat release, cumulative heat release, peak firing pressure, ignition and injection timing and duration of combustion. Furthermore the diagnostic technique is used to derive information for spark advance, spark duration, compression condition etc. The diagnostic technique is based on a thermodynamic two-zone combustion model for spark ignited engines. To examine the effect of AFR on the combustion mechanism a detailed experimental investigation was conducted on an engine (radial, supercharged, air-cooled, eighteen-cylinders) mounted on a test bench. The measurement procedure involved measurements at various operating conditions (load and speed) and various AFR values. During the experimental investigation beyond the conventional test bench measurements, measurements were taken using a fast data acquisition system of cylinder pressure and the electric signal of both spark plugs. Engine diagnosis is established by processing of these measured data. From the results of the diagnosis procedure it is revealed that the diagnosis method provides detailed information for the operating condition of the engine and the values of parameters that cannot be measured on the field. The diagnosis results reveal that the proposed technique can determine the effect of AFR ratio on the combustion mechanism adequately and thus it can be used during engine testing to determine the optimum AFR ratio in combination with the remaining engine settings and mainly spark advance. The results obtained are positive and reveal that the proposed diagnostic technique can be easily applied on any type of spark-ignited engine and especially on aircraft piston engines (i.e. aviation applications), where the accurate estimation of the engine condition and settings is extremely important.