Cylinder Pressure Traces Research Articles

A Diesel Engine Model for Dynamic Drive Cycle Simulations

AbstractThe development and implementation of a diesel engine combustion system simulation model is described. The model is a crank angle based combustion model, which uses the conditions in the intake and exhaust manifolds together with the fuel injection signal from the engine control unit to estimate the in-cylinder pressure throughout a complete combustion cycle. The model is implemented in Matlab. Furthermore, a Simulink coupling has been developed and implemented such that the combustion model can be connected directly to a Simulink mean value model of an engine air system. The coupling makes the combustion model act like a continuous source and a continuous sink in a mean value model. The coupling makes it possible to continuously simulate an engine in steady-state or transient operation, while the combustion model produces estimated cylinder pressure traces for each combustion cycle. This makes it possible to estimate fuel consumption and to couple the model with emission models which use the cylinder pressure or the rate of heat release as input. The model is developed, calibrated and verified using measured data from a 2.4 liter Volvo diesel engine, equipped with a turbocharger, an exhaust gas recirculation system, and a common rail injection system. The combustion model estimates IMEPnet with a correlation factor of 0.995 for the used data. The simulation time is in the range between 1 and 25 milliseconds for one combustion cycle on a standard computer, depending on the implementation.

Evaluation of a combustion model for the simulation of hydrogen spark-ignition engines using a CFD code

The present work deals with the evaluation of a combustion model that has been developed, in order to simulate the power cycle of hydrogen spark-ignition engines. The motivation for the development of such a model is to obtain a simple combustion model with few calibration constants, applicable to a wide range of engine configurations, incorporated in an in-house CFD code using the RNG k– ɛ turbulence model. The calculated cylinder pressure traces, gross heat release rate diagrams and exhaust nitric oxide (NO) emissions are compared with the corresponding measured ones at various engine loads. The engine used is a Cooperative Fuel Research (CFR) engine fueled with hydrogen, operating at a constant engine speed of 600 rpm. This model is composed of various sub-models used for the simulation of combustion of conventional fuels in SI engines; it has been adjusted in the current study specifically for hydrogen combustion. The basic sub-model incorporated for the calculation of the reaction rates is the characteristic conversion time-scale method, meaning that a time-scale is used depending on the laminar conversion time and the turbulent mixing time, which dictates to what extent the combustible gas has reached its chemical equilibrium during a predefined time step. Also, the laminar and turbulent combustion velocity is used to track the flame development within the combustion chamber, using two correlations for the laminar flame speed and the Zimont/Lipatnikov approach for the modeling of the turbulent flame speed, whereas the (NO) emissions are calculated according to the Zeldovich mechanism. From the evaluation conducted, it is revealed that by using the developed hydrogen combustion model and after adjustment of the unique model calibration constant, there is an adequate agreement with measured data (regarding performance and emissions) for the investigated conditions. However, there are a few more issues to be resolved dealing mainly with the ignition process and the applicability of a reliable set of constants for the emission calculations.

Investigating the effect of crevice flow on internal combustion engines using a new simple crevice model implemented in a CFD code

A theoretical investigation is conducted to examine the way the crevice regions affect the mean cylinder pressure, the in-cylinder temperature, and the velocity field of internal combustion engines running at motoring conditions. For the calculation of the wall heat flux, a wall heat transfer formulation developed by the authors is used, while for the simulation of the crevices and the blow-by a newly developed simplified simulation model is presented herein. These sub-models are incorporated into an in-house Computational Fluid Dynamics (CFD) code. The main advantage of the new crevice model is that it can be applied in cases where no detailed information of the ring-pack configuration is available, which is important as this information is rarely known or may have been altered during the engine’s life. Thus, an adequate estimation of the blow-by effect on the cylinder pressure can be drawn. To validate the new model, the measured in-cylinder pressure traces of a diesel engine, located at the authors’ laboratory, running under motoring conditions at four engine speeds were used as reference, together with measured velocity profiles and turbulence data of a motored spark-ignition engine. Comparing the predicted and measured cylinder pressure traces of the diesel engine for all cases examined, it is observed that by incorporating the new crevice sub-model into the in-house CFD code, significant improvements on the predictive accuracy of the model is obtained. The calculated cylinder pressure traces almost coincide with the measured ones, thus avoiding the use of any calibration constants as would have been the case with the crevice effect omitted. Concerning the radial and swirl velocity profiles and the turbulent kinetic energy measured in the spark-ignition engine, the validation process revealed that the developed crevice model has a minor influence on the aforementioned parameters. The theoretical study has been extended by investigating in the same spark-ignition engine, during the induction and compression strokes, the way crevice flow affects the thermodynamic properties of the air trapped in the cylinder.

Fueling an D.I. agricultural diesel engine with waste oil biodiesel: Effects over injection, combustion and engine characteristics

The paper presents the results of a research concerning the use of a biodiesel type fuel in D.I. Diesel engine; the fuel injection system and the engine were tested. The results indicated that the injection characteristics are affected when a blend containing 50% methyl ester and 50% petrodiesel is used as fuel (injection duration, pressure wave propagation time, average injection rate, peak injection pressure). As a result, the engine characteristics are also affected, the use of the biodiesel blend leading to lower output power and torque; the lower autoignition delay and pressure wave propagation time led to changes of the cylinder pressure and heat release traces and to lower peak combustion pressures.

Engine state monitoring and fault diagnosis of large marine diesel engines

The reliable detection of engine malfunctions in order to predict and to plan maintenance intervals is of major importance in various fields of industry. For instance, occurring faults of marine diesel engines which are on the high seas for months may lead to expensive holding times. In this context, condition monitoring systems (CMS) should be able to assess engine health, to predict developing failures, i.e. engine state degradation, and to diagnose failure modes at a low price. In this article, two different thermodynamical model-based approaches to detect two common failure modes – increased blow-by and compression ratio failures – of large diesel engines given cylinder pressure traces with low sampling rate are discussed and compared. Special focus is put on estimation robustness and reliability by excluding the combustion phase and signal parts with high noise level. The proposed algorithms are validated with experimental data.

Modeling of Diesel Combustion, Soot and NO Emissions Based on a Modified Eddy Dissipation Concept

A three-dimensional reacting flow modeling approach is presented for predictions of compression ignition, combustion, NOx and soot emissions over a wide range of operating conditions in a diesel engine. The ignition/combustion model is based on a modified eddy dissipation concept (EDC) which has been implemented into the KIVA-3 V engine simulation code. The modified EDC model is used to represent the thin sub-grid level reaction zone and the small scale molecular mixing processes. In addition, a realistic transition model based on the local normalized fuel mass fraction is implemented to shift from ignition to combustion. The modified EDC model is combined with skeletal n-heptane chemistry and a soot dynamics model, which includes nucleation, surface growth and oxidation and coagulation processes. The NO formation and destruction processes are based on the extended Zeldovich reaction mechanism. The modeling results are calibrated against experimental engine data taken at benchmark conditions. The model is subsequently used to conduct parametric studies of the effects of injection timing and exhaust gas recirculation (EGR) on engine combustion and emissions. Predictions of cylinder pressure traces and heat release rates are in very good agreement with the experimental data (e.g., pressure predictions within 3 bar of the experimental data) for a range of injection timings, EGR rates and speeds. The experimental trends observed for the soot and NO emissions are also reproduced by the modeling results. Overall, the modeling approach demonstrates promising predictive capabilities at reasonable computational costs.

Fast heat release characterization of a diesel engine

Multi-event fuel injection strategies under independently controlled exhaust gas recirculation and intake boost have been applied to produce the heat release patterns that characterize the clean combustion techniques of modern diesel engines. Extensive experimental and analytical comparisons have been performed to better estimate the heat release characteristics from the cylinder pressure traces. A number of heat release models based on the First Principles are compared against a comprehensive heat release model, on the basis of numerical complexity and the ability to characterize the combustion process. Such study indicated that though the estimation from the simplified models is efficient when the heat release is close to the end of the cylinder compression stroke, the simplified models produce shortfalls in estimating the more spread multi-event heat release from the newer combustion systems. A new computationally efficient algorithm, based on the Diesel Pressure Departure Ratio, is proposed to characterize the various heat release patterns with adequate accuracy. The improved heat release analyzing algorithms are further programmed on real-time deterministic devices that process the cylinder pressure data to provide the necessary feedback for the fuel-injection model running on subsequent real-time controllers. The efficacy of the new algorithms has been experimentally demonstrated against selected cases of boost, engine load and exhaust gas recirculation on a modern diesel engine.

Multicylinder engine pressure reconstruction using NARX neural networks and crank kinematics

A NARX neural network is adapted for cylinder pressure trace reconstruction on a multicylinder engine. Following a systematic study to establish the required NARX input information (using measured pressure traces and simulated crank kinematics), two fully recurrent training algorithms are developed and applied to real engine data. These include a back-propagation-through-time algorithm (BPTT) and an extended Kalman filter (EKF). For multi-cylinder engines, two cases are examined, both assuming crank kinematics is obtained from a single shaft-encoder fitted at the forward end of the crankshaft. In one case, a NARX model is constructed to provide an inverse relationship between the kinematics at the encoder location and the pressure trace in an arbitrary cylinder. In the second case, by transforming the kinematics (to emulate a local encoder), a different NARX model is constructed to relate the kinematics at the crank location of a particular cylinder to the corresponding pressure trace. The accuracy and efficiency of both NARX models is examined for application to a three-cylinder in-line DISI engine (in which pressure traces are measured on all cylinders). The paper shows that the computational requirements of training are substantial and, although the efficiency of the EKF algorithm is better than the BPTT, the fitting accuracies are similarly good. For generalization, however (to unseen data), neither method is yet sufficiently accurate (even for steady state engine operation) unless substantially more training data are used to achieve the target accuracy of ± 4 per cent. The overall conclusion of the paper is that the NARX model has the correct architecture for multicylinder pressure reconstruction.

Double-Wiebe function: An approach for single-zone HCCI engine modeling

Single-zone Wiebe-function HCCI combustion models tend to over-predict the peak cylinder pressure. The over-prediction arises because it is not possible for the standard Wiebe function to fully match both the slower combustion (i.e. the large spread of autoignition times) that occurs in the cooler boundary regions adjacent to the walls and the faster combustion (small spread of autoignition times) in the hot core. The slower combustion by the wall is commonly modeled with a multi-zone approach. The aim of this work was to improve the ability of a single-zone model to predict cylinder pressure without introducing a separate wall zone. This was accomplished by using, within a single zone, a double-Wiebe function combustion model in which most of the fuel burns as usual but a minor fraction (typically 10–20%) burns at a reduced rate. In the present article, cylinder pressure traces predicted by using both standard and double-Wiebe functions are compared to experimental pressure traces obtained from a Ricardo Hydra HCCI engine. The best agreement with the experiments was obtained by using double-Wiebe function approach.

Real time NO emissions measurement during cold start in LPG SI engine

Abstract To identify combustion occurrence is very important. Traditionally, cylinder pressure has been used as a criterion of combustion occurrence, but it can be unreliable when identifying lean mixture combustion (there is little difference in the cylinder pressure trace between the firing cycle and motoring cycles at the lean combustion limit). This is particularly important for fuels like LPG, which have a good capacity for lean combustion. In this study, a fast response NO detector, CambustionfNOx400, based on the chemiluminescence method, was used to measure real time NO emissions in order to evaluate the technique as a criterion for establishing combustion occurrence. At the same time, this paper presents an investigation of the characteristics of real time NO emissions of the first firing cycle during cold start in a LPG SI engine to determine the optimal excess air factor of the first firing cycle, and the cylinder pressure and crank shaft speed of the engine were measured and recorded. Test results show that the excess air ratio directly influences the cylinder pressure, engine speed and NO emissions of the first firing cycle. As the excess air coefficient is reduced from the lean misfiring limit, NO emissions increase quickly, then reduce quickly and then reduce slowly. NO emissions generally increase with peak cylinder pressure, even at constant excess air coefficient. Real time NO emissions can be used to identify cylinder combustion and misfire occurrence during engine cranking, even at the dilute combustion limit, and real time NO emission can be used to understand the combustion and misfire occurrence.

Compression ratio estimation based on cylinder pressure data

Four methods for compression ratio estimation based on cylinder pressure traces are developed and evaluated for both simulated and experimental cycles. The first three methods rely upon a model of polytropic compression for the cylinder pressure. It is shown that they give a good estimate of the compression ratio at low compression ratios, although the estimates are biased. A method based on a variable projection algorithm with a logarithmic norm of the cylinder pressure yields the smallest confidence intervals and shortest computational time for these three methods. This method is recommended when computational time is an important issue. The polytropic pressure model lacks information about heat transfer and therefore the estimation bias increases with the compression ratio. The fourth method includes heat transfer, crevice effects, and a commonly used heat release model for firing cycles. This method is able to estimate the compression ratio more accurately in terms of bias and variance. The method is more computationally demanding and is therefore recommended when estimation accuracy is the most important property.

Experimental investigation to develop a methodology for estimating the compression condition of DI Diesel engines

An experimental investigation is conducted to examine the effect of the main parameters influencing the compression stroke of a direct injection Diesel engine. The aim is to develop a methodology that can be used as a diagnostic tool to determine the compression condition of DI Diesel engines. However, conclusions derived from the present investigation can be extrapolated to other types of reciprocating internal combustion engines. The compression stroke itself is an important index concerning engine operation since engine conditions at the end of the compression stroke have a major effect on its overall performance. Such information is especially important for large scale Diesel engines used for stationary or marine applications. In these engines, it is important to develop non-catastrophic methods for estimating the cylinder compression condition without dismantling the engine cylinder. The outcome could be a serious reduction of maintenance costs, since unnecessary labour required for inspection could be avoided. When using measurement techniques, what is usually available is the cylinder pressure trace during the compression stroke. However, it is widely recognized that the compression stroke and peak compression pressure is strongly affected, beyond heat losses, by the initial pressure at the inlet valve closure, the compression ratio and the blowby rate. The last three parameters can vary significantly during engine operation, while the heat losses vary mainly due to engine operating conditions and their effect on the compression stroke can be considered. Thus, the knowledge of the peak compression pressure resulting from the cylinder compression pressure diagram is not adequate to define the cylinder compression condition. For this reason, an experimental investigation is conducted to examine the effect of the initial pressure at the inlet valve closure, the compression ratio and the blowby on the cylinder pressure trace. From analysis of the measured data, it is revealed that each parameter has a different effect on the different parts of the compression pressure trace. As revealed, it is possible to determine the compression condition of an engine cylinder based on the measured cylinder pressure trace.

UTILIZING CYLINDER PRESSURE DATA FOR COMPRESSION RATIO ESTIMATION

Four methods for compression ratio estimation based on cylinder pressure traces are developed and evaluated for simulated and experimental cycles. Three methods rely upon a model of polytropic compression for the cylinder pressure. It is shown that they give good estimates with a small bias at low compression ratios. A variable projection algorithm with a logarithmic norm of the cylinder pressure yields the smallest confidence intervals and shortest computational time for these three methods. This method is recommended when computational time is an important issue. The polytropic pressure model lacks information about heat transfer and therefore the estimation bias increases with compression ratio. The fourth method includes heat transfer, crevice effects, and a commonly used heat release model for firing cycles. This method estimates the compression ratio more accurately in terms of bias and variance. The method is more computationally demanding and thus recommended when estimation accuracy is the most important property. In order to estimate the compression ratio as accurately as possible, motored cycles with high initial pressure should be used.

Compression Ratio Estimation Based on Cylinder Pressure Data

Four methods for compression ratio estimation of an engine from cylinder pressure traces are described and evaluated for both motored and fired cycles. The first three methods rely upon a model of polytropic compression for the cylinder pressure, and it is shown that they give a good estimate of the compression ratio for simulated cycles at low compression ratios. For high compression ratios, this simple model lack the information about heat transfer and the model error causes the estimates to become biased. Therefore a fourth method is introduced where heat transfer and crevice effects are modeled, together with a commonly used heat release model for firing cycles. This method is able to estimate the compression ratio more accurately at low as well as high compression ratios.

The addition of hydrogen to a gasoline-fuelled SI engine

The results of an experimental investigation involving the addition of hydrogen to a gasoline-fuelled SI engine are reported. Up to 66% by volume (3.7% by mass) of hydrogen as fuel was added as part of the air with little modification to the engine. Cylinder pressure traces were used to calculate the indicated mean effective pressure and mass fraction burned. Electrochemical analysers were used to measure the concentration of CO, NO and O 2 in the exhaust. The added hydrogen resulted in improved work output and a reduction in burn duration and cycle-to-cycle variation while operating under lean conditions ( φ<0.85). When operating closer to stoichiometric conditions ( φ>0.85) little difference in engine performance was seen. This dependence of hydrogen addition effect on the fuel/air equivalence ratio was confirmed by analysis of variance tests.

Development of empirically based burning rate sub-models for a natural gas engine

Computer models of engine processes are valuable tools for predicting and analyzing engine performance and allow exploration of many engine design alternatives in an inexpensive fashion. At the present work, experimentally based burning rate sub-models for flame initiation and propagation periods were developed for a natural gas engine. The sub-models do not require any knowledge of the flame shape and propagation speed to calculate the burning rate. The flame initiation sub-model determines where the flame propagation period starts so that experimental spark timing can be used for the calculations. The flame initiation and propagation sub-models were used along with a Zero Dimensional (Zero-D) model to calculate cylinder pressure traces for various engine operating conditions. The Zero-D model is able to match the measured pressure data with less than 8% error in magnitudes if the computations are started at the experimental spark timing. If the flame initiation sub-model is tuned for a specific engine operating condition, then the model is able to match the measured pressure with less than 1% error in magnitudes.

A study of the influence of exhaust gas recirculation and stoichiometry on the heat release in the end-gas prior to knock using rotational coherent anti-Stokes-Raman spectroscopy thermometry

Heat release in the end-gas prior to autoignition was investigated using different experimental methods including transducers for heat flux and pressure as well as rotational coherent anti-Stokes-Raman spectroscopy, which is a laser-based method for non-intrusive instantaneous thermometry of the gas. The time history was examined in the cases of mixtures of various stoichio-metries, where some were diluted with exhaust gas recir-culation (EGR). The measured temperature history was compared with the isentropic temperature calculated from the cylinder pressure trace. This comparison revealed a difference in heat release from low-temperature reactions in the end-gas for the various mixtures tested at a constant indicated mean effective pressure and a fixed position of 50 per cent burnt charge. It is shown that lean mixtures tend to exhibit the highest knock intensity, mainly due to a decrease in specific heat, as compared to the richer mixtures, which result in an earlier knock onset and as a consequence higher knock intensity. Furthermore, the comparison of temperatures indicates that the rich mixtures have a high heat release from low-temperature chemistry, which to some extent negates the higher specific heat of the charge. As a consequence, a slight enrichment of the charge can lead to higher knock intensity in comparison with a stoichiometric mixture. In spite of the lower specific heat of the charge when a stoichiometric charge was diluted with cooled EGR, these mixtures showed a very low tendency to knock.

Cylinder air/fuel ratio estimation using net heat release data

An estimation model which uses the net heat release profile for estimating the cylinder air/fuel ratio of a spark ignition engine is developed. The net heat release profile is computed from the cylinder pressure trace and quantifies the conversion of chemical energy of the reactants in the charge into thermal energy. The net heat release profile does not take heat- or mass transfer into account. Cycle-averaged air/fuel ratio estimates over a range of engine speeds and loads show an RMS error of 4.1% compared to measurements in the exhaust.

Cylinder Air/Fuel Ratio Estimation Using Net Heat Release Data

An estimation model which uses the net heat release profile for estimating the cylinder air/fuel ratio of a spark ignition engine is developed. The net heat release profile is computed from the cylinder pressure trace and quantifies the conversion of chemical energy of the reactants in the charge into thermal energy. The net heat release profile does not take heat- or mass transfer into account. Cycle-averaged air/fuel ratio estimates over a range of engine speeds and loads show an RlVIS error of 4.1% compared to measurements in the exhaust.

Heat Release Analysis of Lean Bum Catalytic Combustion in a Two-Stroke Spark Ignition Engine

A heat release analysis procedure was developed for a two-stroke spark ignition engine. The model was used to calculate instantaneous heat release rates, cumulative heat release and mass fraction burned of base engine and catalytic engine. The combustion chamber of the catalytic engine was coated with a catalyst material by plasma spraying method. The tests were conducted with different air-fuel ratios and heat release analysis was carried out for both base and catalyst coated engines. Engine cylinder pressure traces of 2000 continuous cycles were recorded using a pc based data acquisition system. The average of these traces was calculated and used as input to the heat release model. From the heat release rate various combustion characteristics, such as delay period, start of combustion, end of combustion and combustion duration were calculated for the base and catalytic engines. The results indicate that the heat release model could be used for the calculation of combustion parameters and accurate enough for the present purpose. The calculated combustion parameters indicate that the catalyst induces pre flame reactions of fuel air mixture before combustion, which reduces delay period and increases the combustion rate. The combustion duration of catalytic engine was reduced by 8 degrees at 0.8 equivalence ratio.