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Measurement and Simulation of Instantaneous Emissions of a Heavy Truck Diesel Engine During Transients
Abstract
During the last decades, pollutant emissions from internal combustion engines used for transportation have become a major concern. Today, not only steady state emissions but also emissions during transients are regulated and have to be studied in order to be reduced In this paper we describe a new methodology developed to measure the instantaneous level of gaseous emissions from a internal combustion engine during transients, using an analyzer initially designed for steady state operation. Moreover a new phenomenological thermodynamical combustion model is proposed in order to compute emissions during transients. The results of these two methods are compared on various transients. The measurement method seems to give good results (except for hydrocarbon (HC) measurements), as long as the speed and load variations are not too fast. Otherwise, the frequency of the analyzer which was used becomes the limiting factor. The new combustion heat release developed to simulate transients, coupled with an existing two-zone model for emission calculations, leads to satisfactory results for CO2 and O-2 concentrations and NO, emissions. The agreement with measurements is good for smooth transients and seems promising for faster dynamics. The initial goal was reached, although some improvements are still necessary concerning HC measurements and the fastest transients. These results could be helpful when trying to reduce the amount of pollutant emissions at the exhaust during transients, directly or with after treatment devices.
... Reifarth and Angstrom [16] have used a database of such transient heat release rates within transient models to simulate and compare transient exhaust gas recirculation (EGR) rates for different EGR systems. Tauzia et al. [17] have developed phenomenological models for steady-state and transient heat release coupled with simple zero-dimensional emission models to obtain reasonable agreement over short transient segments. Benz et al. [18] have optimized actuator trajectories by using a quasisteady approach and a mean value model. ...
... Section 3 addresses synchronization of engine events with transient emission measurements to account for transport delay and sensor lag, and demonstrates why it is essential when training empirical models with transient data. The latest state-of-the-art ultrafast transient NO x and CO 2 sensors with a response time in milliseconds used in work reported by Sutela et al. [23] and Peckham et al. [24] are significantly expensive, while using regular steady-state emission analysers, Tauzia et al. [17] involves response time of the order of tens of seconds. The current work relies on commercially available electrochemical NO x sensors installed on the exhaust manifold and light extinction based opacity meters for transient measurements, both of which have delays of the order of 1 s. ...
This is the first part of a study investigating a model-based transient calibration process for diesel engines. The motivation is to populate hundreds of parameters (which can be calibrated) in a methodical and optimum manner by using model-based optimization in conjunction with the manual process so that, relative to the manual process used by itself, a significant improvement in transient emissions and fuel consumption and a sizable reduction in calibration time and test cell requirements is achieved. Empirical transient modelling and optimization has been addressed in the second part of this work, while the required data for model training and generalization are the focus of the current work. Transient and steady-state data from a turbocharged multicylinder diesel engine have been examined from a model training perspective. A single-cylinder engine with external air-handling has been used to expand the steady-state data to encompass transient parameter space. Based on comparative model performance and differences in the non-parametric space, primarily driven by a high engine difference between exhaust and intake manifold pressures (ΔP) during transients, it has been recommended that transient emission models should be trained with transient training data. It has been shown that electronic control module (ECM) estimates of transient charge flow and the exhaust gas recirculation (EGR) fraction cannot be accurate at the high engine ΔP frequently encountered during transient operation, and that such estimates do not account for cylinder-to-cylinder variation. The effects of high engine ΔP must therefore be incorporated empirically by using transient data generated from a spectrum of transient calibrations. Specific recommendations on how to choose such calibrations, how many data to acquire, and how to specify transient segments for data acquisition have been made. Methods to process transient data to account for transport delays and sensor lags have been developed. The processed data have then been visualized using statistical means to understand transient emission formation. Two modes of transient opacity formation have been observed and described. The first mode is driven by high engine ΔP and low fresh air flowrates, while the second mode is driven by high engine ΔP and high EGR flowrates. The EGR fraction is inaccurately estimated at both modes, while EGR distribution has been shown to be present but unaccounted for by the ECM. The two modes and associated phenomena are essential to understanding why transient emission models are calibration dependent and furthermore how to choose training data that will result in good model generalization.
The operation mode of an asymmetric twin-scroll turbine is significantly different from that of a steady state under exhaust pulse feeding conditions, which leads to a more complex matching between a turbine with an engine. In this paper, It was first studied that the matching effect of the flow area ratio of asymmetric twin-scroll to turbine wheel on the pulse energy distribution of asymmetric twin-scroll turbocharged engines. Firstly, It was compared that the deviation between turbine average efficiency on time average testing results and turbine cycle average efficiency based high frequency test results under the background of pulse energy distribution in the scheduling of asymmetric twin-scroll turbocharged engines, as well as a matching method based on pulse energy weight distribution was proposed. Furthermore, the impact of the flow area ratio of scrolls to turbine on matching was studied to further optimize turbine matching. Finally, the optimal and original turbines were tested on the engine to further demonstrate the accuracy and rationality of the results. The results showed that the turbine cycle-average efficiency and the engine fuel economy were improved by about 2%–4% and 0.8%, respectively at the middle and high speeds region of the engine with maintaining equivalent NOx emissions.
Asymmetry, as the most significant characteristic of asymmetric twin-scroll turbines, has a significant effect on the flow characteristics of asymmetric twin-scroll turbines. In this paper, the effect of asymmetry on flow parameters, efficiency, twin-scroll pressure ratio ( SPR), single admission twin-scroll flow parameters ratio ( SSMR) and twin-scroll divide wall of asymmetric twin-scroll turbines were investigated for the first time. First, several turbines with the same total critical section of twin scrolls and different asymmetries were designed, as well as several turbines with the same asymmetric twin scrolls and different heights of the divide wall. Subsequently, these asymmetric twin-scroll turbines were tested and studied on the turbine performance rig. Asymmetry had little influence on turbine flow characteristics under equal admission, but a great impact under partial and single admission. Meanwhile, SMR had a low slope linear relationship with the expansion ratio for every asymmetry turbine. Moreover, the asymmetry was approximately linear with the average single admission twin-scroll pressure ratio ( SSMR ave ), which could be used to guide the early design of asymmetric twin-scroll turbines. Besides, divide wall schemes testing found that the length of divide wall had a certain effect on the SSMR ave , which is a control factor to maintain asymmetric property. Finally, the relation between the expansion ratio of small or large scroll turbines and lg(SPR) was approximately exponential function, and the exponential parameter was strongly correlated with SSMR and SSMR ave , which could be the key parameter reflecting the asymmetry.
This paper first presents a new one-dimensional matching method of an asymmetric twin-scroll turbine with a small scroll bypass wastegate for energy improvement. The proposed methodology provided further consideration for efficiency prediction of the asymmetric twin-scroll turbine and the small scroll exhaust bypass during the matching of model characterization. The efficiency of the small and large scroll turbines was approximately predicted by using 2 times flow parameters of the small and large scroll turbines respectively and turbine efficiency prediction curves. Then according to the matching results of a 9-liter engine, a targeted asymmetric twin-scroll turbine was designed and fabricated, and verified by computational fluid dynamics, performance tests of a turbine and an engine. The results indicate that the prediction efficiency of the asymmetric twin-scroll turbine is in good agreement with that of numerical calculation and performance tests of turbines and engines. Compared with the commonly used large scroll exhaust bypass wastegate, the small one shows better engine performance, and the fuel consumption can be saved about 0.5~1.5% at middle and high engine speeds. In addition, the reasons of which were explored for better understanding of the mechanism accordingly.
3D simulations on a DI diesel engine with high pressure common rail injection system under transient operations with EGR were conducted. The in-cylinder parameters of transient operations were analyzed. Experimental results based on time were converted into the discrete points based on cycle. NOx emissions were analyzed by volume, duration of in-cylinder high temperature area and φ-T diagram. Simulation results of separated transient cycle agree with that of the corresponding experimental data. NOx emissions decreases under the increasing torque process while soot emissions increase substantially as being explained by φ-T diagram where in-cylinder equivalence ratio and temperature approach to the soot area and retreat to NOx area when loads increased. Uniformity of cylinder mixture was analyzed by Lorenz curve. Under transient conditions, soot emission deterioration is from the increased heterogeneity of the in-cylinder fuel-air mixture compared with steady condition.
Dimensional modeling, GT-Power in particular, has been used for two related purposes-to quantify and understand the inaccuracies of transient engine flow estimates that cause transient smoke spikes and to improve empirical models of opacity or particulate matter used for engine calibration. It has been proposed by dimensional modeling that exhaust gas recirculation flow rate was significantly underestimated and volumetric efficiency was overestimated by the electronic control module during the turbocharger lag period of an electronically controlled heavy duty diesel engine. Factoring in cylinder-to-cylinder variation, it has been shown that the electronic control module estimated fuel-Oxygen ratio was lower than actual by up to 35% during the turbocharger lag period but within 2% of actual elsewhere, thus hindering fuel-Oxygen ratio limit-based smoke control. The dimensional modeling of transient flow was enabled with a new method of simulating transient data in which the manifold pressures and exhaust gas recirculation system flow resistance, characterized as a function of exhaust gas recirculation valve position at each measured transient data point, were replicated by quasi-static or transient simulation to predict engine flows. Dimensional modeling was also used to transform the engine operating parameter model input space to a more fundamental lower dimensional space so that a nearest neighbor approach could be used to predict smoke emissions. This new approach, intended for engine calibration and control modeling, was termed the "nonparametric reduced dimensionality" approach. It was used to predict federal test procedure cumulative particulate matter within 7% of measured value, based solely on steady-state training data. Very little correlation between the model inputs in the transformed space was observed as compared to the engine operating parameter space. This more uniform, smaller, shrunken model input space might explain how the nonparametric reduced dimensionality approach model could successfully predict federal test procedure emissions when roughly 40% of all transient points were classified as outliers as per the steady-state training data.
Model-based calibration of steady-state engine operation is commonly performed with highly parameterized empirical models that are accurate but not very robust, particularly when predicting highly nonlinear responses such as diesel smoke emissions. To address this problem, and to boost the accuracy of more robust non-parametric methods to the same level, GT-Power was used to transform the empirical model input space into multiple input spaces that simplified the input-output relationship and improved the accuracy and robustness of smoke predictions made by three commonly used empirical modeling methods: Multivariate Regression, Neural Networks and the k-Nearest Neighbor method. The availability of multiple input spaces allowed the development of two committee techniques: a 'Simple Committee' technique that used averaged predictions from a set of 10 pre-selected input spaces chosen by the training data and the "Minimum Variance Committee" technique where the input spaces for each prediction were chosen on the basis of disagreement between the three modeling methods. This latter technique equalized the performance of the three modeling methods. The successively increasing improvements resulting from the use of a single best transformed input space (Best Combination Technique), Simple Committee Technique and Minimum Variance Committee Technique were verified with hypothesis testing. The transformed input spaces were also shown to improve outlier detection and to improve k-Nearest Neighbor performance when predicting dynamic emissions with steady-state training data. An unexpected finding was that the benefits of input space transformation were unaffected by changes in the hardware or the calibration of the underlying GT-Power model.
Particulate matter spikes occurring during transient engine operation have important health implications. This paper investigates the root cause of particulate matter spikes in modern electronically controlled diesel engines that impose strict fuel-Oxygen ratio limits during the turbocharger lag period. It is proposed that these spikes can be significantly reduced by improved estimation of transient charge flow through the engine. Through transient data analysis and with the aid of transient data based empirical models, it has been shown that the fuel-Oxygen ratio restrictions imposed by contemporary engine controllers are ineffective during transients because of temporary but large differences between exhaust and intake manifold pressures during aggressive transients resulting in inaccurate volumetric efficiency and charge flow estimation. Steady state experiments with artificially generated high engine manifold pressure differentials have been conducted to support this hypothesis. The engine manifold pressure differential hypothesis is a consequence of previous investigations to explain the baffling inability of empirical data based models to predict the magnitudes of transient particulate matter spikes. Accurate volumetric efficiency estimation during transients can make the fuel-Oxygen ratio limits more effective at reducing opacity spikes. It would also make model based transient calibration more useful by increasing the accuracy of particulate matter models and by directing any dynamic optimization process to mould calibratable surfaces to minimize engine manifold pressure differential spikes. Fuel efficiency benefits due to lower pumping losses during transients and lower regeneration penalties would also result.
Smoke spikes occurring during transient engine operation have detrimental health effects and increase fuel consumption by requiring more frequent regeneration of the diesel particulate filter. This paper proposes a decision tree approach to real-time detection of smoke spikes for control and on-board diagnostics purposes. A contemporary, electronically controlled heavy-duty diesel engine was used to investigate the deficiencies of smoke control based on the fuel-to-oxygen-ratio limit. With the aid of transient and steady state data analysis and empirical as well as dimensional modeling, it was shown that the fuel-to-oxygen ratio was not estimated correctly during the turbocharger lag period. This inaccuracy was attributed to the large manifold pressure ratios and low exhaust gas recirculation flows recorded during the turbocharger lag period, which meant that engine control module correlations for the exhaust gas recirculation flow and the volumetric efficiency had to be extrapolated. The engine control module correlations were based on steady state data and it was shown that, unless the turbocharger efficiency is artificially reduced, the large manifold pressure ratios observed during the turbocharger lag period cannot be achieved at steady state. Additionally, the cylinder-to-cylinder variation during this period were shown to be sufficiently significant to make the average fuel-to-oxygen ratio a poor predictor of the transient smoke emissions. The steady state data also showed higher smoke emissions with higher exhaust gas recirculation fractions at constant fuel-to-oxygen-ratio levels. This suggests that, even if the fuel-to-oxygen ratios were to be estimated accurately for each cylinder, they would still be ineffective as smoke limiters. A decision tree trained on snap throttle data and pruned with engineering knowledge was able to use the inaccurate engine control module estimates of the fuel-to-oxygen ratio together with information on the engine control module estimate of the exhaust gas recirculation fraction, the engine speed, and the manifold pressure ratio to predict 94% of all spikes occurring over the Federal Test Procedure cycle. The advantages of this non-parametric approach over other commonly used parametric empirical methods such as regression were described. An application of accurate smoke spike detection in which the injection pressure is increased at points with a high opacity to reduce the cumulative particulate matter emissions substantially with a minimum increase in the cumulative nitrogrn oxide emissions was illustrated with dimensional and empirical modeling.
This is the second part of a study investigating a model-based transient calibration process for diesel engines. The first part addressed the data requirements and data processing required for empirical transient emission and torque models. The current work focuses on modelling and optimization. The unexpected result of this investigation is that when trained on transient data, simple regression models perform better than more powerful methods such as neural networks or localized regression. This result has been attributed to extrapolation over data that have estimated rather than measured transient air-handling parameters. The challenges of detecting and preventing extrapolation using statistical methods that work well with steady-state data have been explained. The concept of constraining the distribution of statistical leverage relative to the distribution of the starting solution to prevent extrapolation during the optimization process has been proposed and demonstrated. Separate from the issue of extrapolation is preventing the search from being quasi-static. Second-order linear dynamic constraint models have been proposed to prevent the search from returning solutions that are feasible if each point were run at steady state, but which are unrealistic in a transient sense. Dynamic constraint models translate commanded parameters to actually achieved parameters that then feed into the transient emission and torque models. Combined model inaccuracies have been used to adjust the optimized solutions. To frame the optimization problem within reasonable dimensionality, the coefficients of commanded surfaces that approximate engine tables are adjusted during search iterations, each of which involves simulating the entire transient cycle. The resulting strategy, different from the corresponding manual calibration strategy and resulting in lower emissions and efficiency, is intended to improve rather than replace the manual calibration process.
The present work aims to analyze the thermal and the energetic performances of an aftertreatment system with unidirectional and periodic reversal flow within the device. To this purpose a single-channel one-dimensional model was developed in order to assess the heat exchange between the aftertreatment system and the exhaust gas. Furthermore, the temperature profiles of the gas and solid phase were computed and the calculated temperatures were adopted to characterize the energy effectiveness of the aftertreatment system. The comparison between different control modes showed an increase in the heat retention efficiency of the system with reverse flow at low engine load conditions. Conversely, the system with passive thermal management presented higher temperatures of the monolith during the warm-up operations. Furthermore, the influence of unburned hydrocarbons oxidation on the effectiveness of the aftertreatment system was evaluated and the significant influence of the cycle time and the monolith length on the system performance was shown. Finally, the gas residence time was evaluated for different operating conditions. Copyright © 2008 John Wiley & Sons, Ltd.
As widely recognized the direct injection heavy-duty diesel engine is the most efficient powertrain system for trucks, lories and other heavy-duty vehicles. This result from its relatively low specific fuel con-sumption compared to other existing thermal engines. Taking this under consideration it remains a serious prob-lem, its relatively high, compared to future legislation, NOx and particulate emissions. Manufacturers have pro-posed various solutions towards this problem. Two are the main categories proposed, improvement of the combustion process to control directly the formation of pollutants inside the combustion chamber and the use of aftertreatment technologies to reduce pollutants at the engine exhaust. In the present work we will concentrate our efforts on the first category by examining the technique of post fuel injection. For this reason a multi-zone phenomenological model is used to examine the effect of post fuel injection on pollutants emissions and bsfc. The study is conducted using a single cylinder heavy-duty test diesel engine capable of withstanding relatively high peak combustion pressures. The simulation model has been used to examine the effect of post fuel injection at various operating conditions corresponding to key operation points of the engine under question. During the investigation, various injection timings are considered setting the peak combustion pressure limit to 200-220 bar. In all cases, the effect of the interval between the main and the post fuel injection, is examined. From the analy-sis of results, important information is derived concerning the effect of post fuel injection parameters on engine performance and emissions. The results are given in the form of bsfc-NO and PM-NO curves to obtain a clear picture of the effect of post injection. Furthermore results are provided concerning the pollutant formation mechanism i.e. Soot and NO formation history inside the combustion chamber. As revealed post injection seems to have no serious effect on NO emissions since it occurs at the late stages of combustion, but on the other hand 2 D. it seems to have a serious effect on PM emission. The effect on PM emission depends on the interval between the main and the post fuel injection. Post injection has a small penalty on bsfc but this is compensated by the se-rious reduction of PM. The results are promising and it remains to verify them using experimental data. Another important outcome of the present investigation is that phenomenological modeling is a promising tool to study such cases since it is very fast and can contribute to the reduction of development cost. Of course these models cannot be directly compared to multi-dimensional sophisticated ones since the last concentrate on the detailed modeling of the various processes occurring inside the cylinder, but in the time being it is the most efficient way to conduct overall engine performance and pollutant emission simulations where a great number of parameters are involved. For this reason we believe that the use of such models is a promising tool for engineers who want qualitative results before conducting a more detailed investigation using CFD mo dels.
A quasi -dimensional, multi-zone, direct injection (DI) diesel combustion model has been developed and implemented in a full cycle simulation of a turbocharged engine. The combustion model accounts for transient fuel spray evolution, fuel-air mixing, ignition, combustion and NO and soot pollutant formation. In the model, the fuel spray is divided into a number of zones, which are treated as open systems. While mass and energy equations are solved for each zone, a simplified momentum conservation equation is used to ca lculate the amount of air entrained into each zone. Details of the DI spray, combustion model and its implementation into the cycle simulation of Assanis and Heywood (1) are described in this paper. The model is validated with experimental data obtained in a constant volume chamber and engines. First, predictions of spray penetration and spray angle are validated against measurements in a pressurized constant volume chamber. Subsequently, predictions of heat release rate, as well as NO and soot emissions are compared with experimental data obtained from representative heavy-duty, turbocharged diesel engines. It is demonstrated that the model can predict the rate of heat release and engine performance with high fidelity. However, additional effort is require d to enhance the fidelity of NO and soot predictions across a wide range of operating conditions.
Instantaneous emissions measurements on chassis dynamometers and engine test benches are becoming increasingly normal for environmental emission factor calculation. Modern exhaust gas analysers allow measurement at a rate of one sample per second, thus creating the impression that the emissions information recorded reflects that precision. Normally, the time delay between the car and the analysers is considered to be constant and compensated for accordingly. In reality, this time delay varies by more than three seconds depending on the engine load. Moreover, emission peaks are smoothed by turbulence during transport. The analyser's dynamics smooth the signals even more. For example, an emission peak of one second is flattened to a three-second peak in raw gas measurement, and to a very low hill of about ten seconds in diluted gas measurement. If emissions measurements are to be correlated to actual driving conditions, the variable time delays and the smoothing must be compensated for. To achieve this, the time delay at a given time can be calculated by dividing the volume of the exhaust system by the actual exhaust flow. ''Smoothing'' is compensated for by adopting a system theory-based approach. It can be described with a linear differential equation, which can be ''inverted'' in an offline procedure.
Recently, an on-board measurement system that is capable of measuring real-time mass emission of nitrogen oxides (NOx), fuel consumption, road load, and engine output simultaneously has been developed. The system consists of a data recorder and a variety of sensors including an air-to-fuel ratio sensor and a NOx sensor. The system can be placed on the passenger seat and operated without external power. Test results of NOx mass emission and fuel consumption obtained by on-road measurements of diesel vehicles have been already reported. In the present investigation, a total hydrocarbon (THC) analyzer using flame ionization detector (FID) and a smoke-meter using opacity method are added to the on-board measurement system, because THC and particulate matters (PM) are paid much attention as well as NOx. The on-board measurement system was installed in a diesel vehicle and measurements were taken on a chassis dynamometer and on public road. As a result, it can be shown that the on-board measurement system can measure mass emission of THC as well as NOx or other items. Mass emission of PM is also possible to be obtained from smoke-meter output, by applying a calibration line that is pre-determined by comparing with conventional filtering method. Evaluation of the results, using a chassis dynamometer and CVS-tunnel system as a reference, reveals fair correlation : from -3 % to 8 % for THC mass emission, and from -10 % to 12 % for PM mass emission. At the on-road test, it has been observed that the patterns of THC and PM mass emission during on-road runs show good agreement with those of NOx mass emission and fuel consumption. And the effects of the EGR function for NOx and PM mass emission have been clearly observed by the on-board measurement system.
Conventional exhaust gas analyzers are of limited use in transient engine testing as the dynamics of the analyzers cause distortion of the emissions measurement during transients. An advanced technique is presented which uses signal reconstruction to determine the actual emissions during engine transients from the distorted output of a conventional exhaust gas analyzer. The reconstruction technique is based on the design of a finite horizon filter which is a dual of generalized predictive control theory. Results are presented which demonstrate the use of this technique for reconstruction of instantaneous emissions from a diesel engine over a part of the US heavy duty test cycle. The results show that the reconstructed emissions recover significant information which is otherwise obscured by the distortion introduced by the analyzer dynamics. In addition, the reconstructed emissions can be corrected for exhaust gas mass flow rate, enabling a more accurate evaluation of the instantaneous and cumulative mass emissions during complex transient cycles to aid in engine development. (A)
Simple air-path models for modern (VGT/EGR equipped) diesel engines are in common use, and have been reported in the literature. This paper addresses some of the shortcomings of control-oriented models to allow better prediction of the cylinder charge properties. A fast response CO2 analyzer is used to validate the model by comparing the recorded and predicted CO2 concentrations in both the intake port and exhaust manifold of one of the cylinders. Data showing the recorded NOx emissions and exhaust gas opacity during a step change in engine load illustrate the spikes in both NOx and smoke seen during transient conditions. The predicted cylinder charge properties from the model are examined and compared with the measured NOx and opacity. Together, the emissions data and charge properties paint a consistent picture of the phenomena occurring during the transient. Alternative strategies for the fueling and cylinder charge during these load transients are investigated and discussed. Experimental results are presented showing that spikes in both NOx and smoke can be avoided at the expense of some loss in torque response. Even if the torque response must be maintained, it is demonstrated that it is still possible to eliminate spikes in NOx emissions for the transient situation being examined.
The Tapered Element Oscillating Microbalance (TEOM) measures captured particle mass continuously on a small filter held on an oscillating element. In addition to traditional filter-based particulate matter (PM) measurement, a TEOM was used to characterize PM from the dilute exhaust of trucks examined in two phases (Phase 1.5 and Phase 2) of the Coordinating Research Council (CRC) Heavy-Duty Vehicle Emissions Inventory Project E-55/E-59. Test schedules employed were the Heavy Heavy-Duty Diesel Truck (HHDDT) test schedule that consists of four modes (Idle, Creep, Transient and Cruise), the HHDDT Short (HHDDT-S) which represents high-speed freeway operation, and the Heavy-Duty Urban Dynamometer Driving Schedule (UDDS). TEOM results were on average 6% lower than those from traditional particulate filter weighing. Data (in units of g/cycle) were examined by plotting cycle-averaged TEOM mass against filter mass. Regression (R2) values for these plots were from 0.88 to 0.99. The TEOM/filter mass ratio varied most, and correlation was the worst, for the Idle and the HHDDT-S but it was steady for the UDDS, Creep, Transient, and Cruise cycles. In the case of Idle, poor correlation may be attributed to the variation in organic fraction of the PM between vehicles, coupled with differences in filter face temperatures between the TEOM and traditional filter. Slopes and intercepts varied only slightly between the UDDS, Creep, Transient, and Cruise, and between vehicle test weights. This implies that TEOM data may be used with some confidence to report PM mass from a portion of a test schedule, and that TEOM data can act as a check on, or early screen for, PM filter data when multiple runs are not performed. For the case of the HHDDT-S, it was found using TEOM data that the cruising section of the schedule had distance-specific PM emissions that were 10% lower than for the whole schedule. The acceleration and deceleration portions of the schedule had PM emissions that were 33% higher than for the whole schedule. In this way, modal behavior can be extracted. In previous research, when TEOM data were not available, the authors used continuous carbon monoxide (CO) data to proportion PM over a cycle. Although there was no overall (fleet) relationship between CO and PM integrated over the test schedule, data taken from a single truck executed through six different schedules showed a strong relationship between CO and PM. In this case, it is likely that higher CO production is in sympathy with higher elemental carbon production in the cylinder.
Transient engine tests were performed to investigate behavior of transient emissions - hydrocarbon (HC) and oxides of Nitrogen (NOx) - in a 2.4L turbocharged four cylinder High Speed Direct Injection (HSDI) diesel engine which is coupled to a hydrostatic transient dynamometer. Emissions were measured from one exhaust port 5 cm downstream of the exhaust valve and from the exhaust pipe 14 cm below the wastegate of the turbocharger. These measurements were made with fast response HC and NOx measurement analyzers. The experiments were conducted by increasing torque at constant speed and by increasing speed at constant torque, in conventional diesel combustion regions. The emissions from the two locations are compared. The transient effects of Exhaust Gas Recirculation (EGR) rates and injection timing on HC and NOx are described and the effects of linear and step load change on emissions are compared. Base EGR was set with an EGR valve on the engine; the position of the valve was then held constant throughout the transient. The pressure history in one of the cylinders was measured as well. The results show that peak emissions of NOx occurred when a step load change was applied for constant speed and constant torque cases at low EGR levels, but there were no evident step load change effects on NOx when higher EGR levels were used. NOx emissions were very sensitive to transient operation of changing injection timing and EGR rates for constant speed and constant torque cases. The HC measurement showed little sensitivity to transients when the EGR valve was closed. The HC emission sensitivity to transients increased dramatically when EGR rate was increased. It should be noted that injection timing and EGR rate affected engine torque and speed for a constant quantity of fuel injected.
A phenomenological description, or "conceptual model," of how direct-injection (DI) diesel combustion occurs has been derived from laser-sheet imaging and other recent optical data. To provide background, the most relevant of the recent imaging data of the author and co-workers are presented and discussed, as are the relationships between the various imaging measurements. Where appropriate, other supporting data from the literature is also discussed. Then, this combined information is summarized in a series of idealized schematics that depict the combustion process for a typical, modern-diesel-engine condition. The schematics incorporate virtually all of the information provided by our recent imaging data including: liquid- and vapor-fuel zones, fuel/air mixing, autoignition, reaction zones, and soot distributions. By combining all these elements, the schematics show the evolution of a reacting diesel fuel jet from the start of fuel injection up through the first part of the mixing-controlled burn (i.e. until the end of fuel injection). In addition, for a "developed" reacting diesel fuel jet during the mixing-controlled burn, the schematics explain the sequence of events that occurs as fuel moves from the injector downstream through the mixing, combustion, and emissions-formation processes. The conceptual model depicted in these schematics also gives insight into the most likely mechanisms for soot formation and destruction and NO formation during the portion of the DI diesel combustion event discussed.
This paper describes a diesel engine simulation code, named SELENDIA, jointly developed by Ecole Centrale de Nantes, France, and the University of New Orleans. The adopted models for steady-state and transient response simulation are briefly introduced in addition to various validation results. The capabilities of the code are illustrated by a study regarding the transient response of a sequentially turbocharged marine diesel engine as well as the simulation of engine performance under extreme conditions and the investigation of engine pollutant emissions.
A mathematical model of a spray combustion in direct-injection diesel engines has been developed to predict engine performance, thermal efficiency and pollutant emissions. Injected fuel spray was divided into many small packages. Gas and fuel droplet temperatures and evaporated mass of fuel in each package were computed. In considering the complete air-fuel jet mixing process and temperature in each package, the model also enabled subsequent spatial and temporal history of burning rate, local temperature and air-fuel ratio to be calculated.
This paper presents a method to estimate instantaneous diesel engine emissions during transients using analytical means usually adopted for steady state investigations. The initial emphasis is on the inability of the conventional analysis systems to directly provide instantaneous levels of gaseous emissions during transients. In the ensuing section, a signal reconstruction technique used to rebuild instantaneous pollutant emissions at the engine exhaust is described. This reconstruction is based on a transfer function, which is the ratio of known measured and applied pollution signals. As a validation of this technique, the inversion of the transfer function is then applied to measurements obtained during basic tests consisting of steps and ramps. Finally, a method for estimating diesel particulates during transients through a correlation established from the measurements of carbon monoxide and smoke opacity is presented.
The design and development of internal combustion engines, and by extension of complete powertrains for ground vehicles, constitute a particularly complex, costly and time consuming task. As a result, numerical simulation is now commonly used by engine manufacturers and vehicle designers in addition to test bench experiments. Engine simulation codes can be divided into three main categories, with very different objectives and levels of complexity: CFD codes, thermodynamic codes and real time codes. This paper presents the MERIMEE simulation code, which belongs to the second category (MERIMEE is the French acronym for Computer Research and Study Model for Engines and their Equipment). Jointly developed by Ecole Centrale de Nantes (for the models) and the CS-SI Company (for the software development) it is used by ETAS (French Army) for the development and study of complete powertrains designed for military ground propulsion. The main models used to simulate the engine behavior are first briefly described. Then, the software architecture, the interface as well as the programming and numerical aspects are described. Finally, some significant results are shown and compared with experimental data. They deal with steady state and transient engine behavior in addition to the evaluation of pollutant emissions.
The objective of this work is the development of a zero-dimensional Diesel combustion model. After the development of a model based on the apparent combustion time for the central phase of the quasi-steady Diesel diffusion combustion [Appl. Therm. Eng. 23 (2003)], this second part describes the work of generalization of the model for the final and initial transient phases of the diffusion combustion. For this purpose, those transient phases are analyzed mainly on the basis of the results of CFD calculations for pulsed gas jets. The generalization for the final transient diffusion combustion phase is based on the analysis of the evolution of the turbulent effective viscosity dissipation at the end of the injection process. For the initial transient diffusion combustion phase the work is based on the analysis of the air/fuel mixture at the beginning of the injection process. The result is a zero-dimensional model capable of predicting the diffusion combustion in a Diesel engine. The validation of the proposed model has been performed on both a high speed Diesel engine and a heavy duty Diesel engine.
This paper reports our efforts to develop an instrument, TG-1, to measure particulate emissions from diesel engines in real-time. TG-1 while based on laser-induced incandescence allows measurements at 10 Hz on typical engine exhausts. Using such an instrument, measurements were performed in the exhaust of a 1.7L Mercedes Benz engine coupled to a low-inertia dynamometer. Comparative measurements performed under engine steady state conditions showed the instrument to agree within ′12% of measurements performed with an SMPS. Moreover, the instrument had far better time response and time resolution than a TEOM® 1105. Also, TG-1 appears to surpass the shortcomings of the TEOM instrument, i.e., of yielding negative values under certain engine conditions and, being sensitive to external vibration.
This paper presents the SELENDIA code designed for the simulation of marine diesel engines. Various measured and simulated results are compared for the performance of a sequentially turbo-charged marine diesel engine during a switch from one to two turbochargers. The results show a good agreement between measured and simulated data. Surge loops that are experimentally observed in case of an anomaly are analyzed using simulated results. Finally, the predictive capabilities of the simulation code are utilized to investigate the influence of the inlet manifold volume on the engine and air charging system performance with a special focus on compressor surge.
A quasi-dimensional multi-zone combustion model for direct injection diesel engines has been developed and subsequently evaluated using test results from a PA6 engine. In the new model, fuel spray is divided into a number of zones, which are treated as open thermodynamic systems exchanging mass and energy with the surrounding air. This paper pays particular attention to the fuel evaporation process whereby a detailed evaporation model is developed to predict the fuel evaporation rate. The effects of both collision and aggregation of fuel droplets have been included in the fuel evaporation mechanism. The theory of grouping of fuel droplets and interference areas among droplets is used to gain more accurate fuel evaporating and burning rates for the engine. The results from the simulation studies have shown good agreement with the measurements from the experimental engine. In-cylinder pressure and temperature are given particular attention in this study. The developments reported in this paper lead to a better understanding of the underlying physical mechanisms and the effects of various parameters on engine combustion. This work also presents a methodology for the development of a reliable but simple multi-zone model. Conclusions have been reached that the developed model is able to predict the rate of heat release and engine performance with a high accuracy.
Heavy trucks contribute significantly to the overall air pollution, especially NOx and PM emissions. Models to predict the emissions from heavy trucks in real world on road conditions are therefore of great interest. Most such models are based on data achieved from stationary measurements, i.e. engine maps. This type of "quasi stationary" models could also be of interest in other applications where emission models of low complexity are desired, such as engine control and simulation and control of exhaust aftertreatment systems. In this paper, results from quasi stationary calculations of fuel consumption, CO, HC, NOx and PM emissions are compared with time resolved measurements of the corresponding quantities. Measurement data from three Euro 3-class engines is used. The differences are discussed in terms of the conditions during transients and correction models for quasi stationary calculations are presented. Simply using engine maps without transient correction is not sufficient. For the engines studied, accumulated errors of up to 60-70% are common before correction. Earlier work in this field has mainly been focused on statistical correction models of accumulated emissions. The transient correction model presented in this paper uses stepwise correction and has a physical interpretation. The delay introduced by the turbocharger during transients results in lower air flows and hence lower air-fuel ratios, than predicted from engine maps. A delay time and a corresponding transient air-fuel equivalence ratio (λ) is estimated in each time step and is used for compensation of the emissions. Another important aspect of models for simulating real world emissions is generality, whether a common emission model can be used for all engines of a given emission classification. Differences between the engines in this study are discussed.
This paper reports our efforts to develop an instrument, TG-1, to measure particulate emissions from diesel engines in real-time. TG-1 while based on laser-induced incandescence allows measurements at 10 Hz on typical engine exhausts. Using such an instrument, measurements were performed in the exhaust of a 1.7L Mercedes Benz engine coupled to a low inertia dynamometer. Comparative measurements performed under engine steady state conditions showed the instrument to agree within {+-}12% of measurements performed with an SMPS. Moreover, the instrument had far better time response and time resolution than a TEOM{reg_sign} 1105. Also, TG-1 appears to surpass the shortcomings of the TEOM instrument, i.e., of yielding negative values under certain engine conditions and, being sensitive to external vibration.
The Bureau of Mines, U.S. Department of the Interior, conducts research to reduce exposure of miners to exhaust emissions of diesel-powered mining equipment. Conventional sampling and instrumentation techniques used to measure emissions over a research duty cycle distort the signal generated by time variation of the concentration of gases in the exhaust. Delays up to 30 sec, effective integration times, up to 2.9 sec, and dispersions up to 1.4 sec are observed. This book reports numerical techniques that make it possible to infer the actual variation of concentration in the exhaust on a time scale of about 1 sec. These techniques are used to evaluate the product of concentration and flow to yield accurate total gaseous emission during a test.
The recent developments in heavy duty Diesel engine technology, in particular high pressure, electronically controlled flexible injection devices, have made the first empirical models for the calculation of combustion heat release obsolete. The aim of this paper is to present a new phenomenological, flexible heat release model for modern turbocharged heavy duty Diesel engines. First of all, a literature survey is made, analysing the various kinds of existing models. The second part of the paper is a detailed description of the new model. In the first section, the main equations are given and it is explained how the model was designed. The second section deals with the parameterisation of the model. The third part presents the main results of the model, which are compared to CFD calculations and experimental measurements. Finally, a brief summary of the main results is made, along with perspectives for future work.
In this study, a procedure was applied for the performance of real-time emissions measurement at engine transient tests. The measurement of gaseous emissions from raw exhaust was done according to the standard ISO16183:2002 and the particulate mass emission was determined by an alternative method based on the measurement of smoke opacity and hydrocarbon emission during the transient test for further conversion to particulate mass. The method for calculating particle mass was validated by comparison with experimental data obtained by application of the standard gravimetric method.A measurement strategy, including engine preconditioning and control of ambient temperature, was applied to improve measurements. For the analysis of results, the time misalignment of the measurements was corrected by the calculation of the delay times produced as a result of the measurement systems configuration.The measurement procedure was applied to two cases of cycles UDC: with and without glow plug inside the cylinder of a light duty Diesel engine. The time evolution of each pollutant was analyzed to get understanding of which stages of the cycle produce more pollution and the comparison between both cycles was done by using the exhaust emissions integrated during the tests.
The aim of this work is to identify and quantify the influence of injection parameters and running conditions on Diesel combustion. This theoretical–experimental analysis is the basis for the development of a zero-dimensional Diesel combustion model. The objective of this first part is to analyze the physical variables and processes that control the central phase of the quasi-steady Diesel diffusion combustion. For that purpose, a parameter as the apparent combustion time (ACT) characteristic of a diffusion combustion process has been used. This parameter allows to obtain explicit relations between, on the one hand, the injection rate law and in-cylinder conditions (air density, oxygen concentration…), and on the other hand, the rate of heat release. Results show a good correlation between the ACT and the instantaneous values of in-cylinder gas density, injection velocity, oxygen concentration and the nozzle diameter.
Measurement and Prediction of Transient NOx Emissions in DI Diesel Engines
- C Arcoumanis
- C S Jou
Arcoumanis, C., and Jou, C. S., 1992, "Measurement and Prediction of Transient NO x Emissions in DI Diesel Engines," ImechE Paper No. C448/039, pp.
97-105.
Time Series Analysis of Diesel Exhaust Gas Emissions Under Transient Operation
- N Myamoto
- H Ogawa
- M Shibuya
- N Fuwa
Myamoto, N., Ogawa, H., Shibuya, M., Fuwa, and N., 1993, "Time Series
Analysis of Diesel Exhaust Gas Emissions Under Transient Operation," SAE
Technical Paper No. 930976, pp. 724-731.
Evaluation of Five Instruments for the Real-Time Measurement of Diesel Particulate Mass Emissions
- H Moosmüller
- W P Arnott
- C F Rogers
- J L Bowen
- J Gillies
- W R Pierson
- J F Collins
- T D Durbin
- J M Norbeck
Moosmüller, H., Arnott, W. P., Rogers, C. F., Bowen, J. L., Gillies, J., Pierson,
W. R., Collins, J. F., Durbin, T. D., and Norbeck, J. M., 2000, "Evaluation of
Five Instruments for the Real-Time Measurement of Diesel Particulate Mass
Emissions," Proceedings of the Tenth CRC On-Road Vehicle Emissions Work
Shop, Atlanta, GA.
Comparison of Heavy-Duty Truck Diesel Particulate Matter Measurement: Teom and Traditional Filter
- S Xu
Xu, S., 2005, "Comparison of Heavy-Duty Truck Diesel Particulate Matter
Measurement: Teom and Traditional Filter," 2005 SAE Brasil Fuels and Lubricants Meeting, Rio De Janiero, Brazil, May 2005, SAE Paper No. 2005-01-2153.
Prediction of Turbulence Controlled Combustion in Diesel Engines
- F G Chmela
- M Engelmayer
- G Pirker
- A Wimmer
Chmela, F. G., Engelmayer, M., Pirker, G., and Wimmer, A., 2004, "Prediction
of Turbulence Controlled Combustion in Diesel Engines," THIESEL 2004
Conference on Thermo-and Fluid Dynamic Processes in Diesel Engines.
Contribution à l’Étude des Émissions Polluantes et des Moyens de Dépollution dans un Moteur Diesel Suralimenté en Fonctionnement Transitoire
- N Thouvenel
Thouvenel, N., 2004, "Contribution à l'Étude des Émissions Polluantes et des
Moyens de Dépollution dans un Moteur Diesel Suralimenté en Fonctionnement Transitoire," Ph.D. thesis, Ecole Centrale de Nantes, France.
Two Zone Calculation Model for the Prediction of NO Emissions From Diesel Engines
- G Heider
- K Zeilinger
- G Woschni
Heider, G., Zeilinger, K., and Woschni, G., 1995, "Two Zone Calculation
Model for the Prediction of NO Emissions From Diesel Engines," Proceedings
of 21st Cimac Conference, Interlaken, Switzerland, Jun. 1995.
Evaluation of Five Instruments for the Real-Time Measurement of Diesel Particulate Mass Emissions
- Moosmüller
Two Zone Calculation Model for the Prediction of NO Emissions From Diesel Engines
- Heider
Pollutants Instantaneous Measurements and Data Analysis of Engine in the Loop Tests
- A Broatch
- J M Lujàn
- J R Serrano
- B Pla