Combustion Phasing Control Research Articles

Diesel-Minimal Combustion Control of a Natural Gas-Diesel Engine

This paper investigates the combustion phasing control of natural gas-diesel engines. In this study, the combustion phasing is influenced by manipulating the start and the duration of the diesel injection. Instead of using both degrees of freedom to control the center of combustion only, we propose a method that simultaneously controls the combustion phasing and minimizes the amount of diesel used. Minimizing the amount of diesel while keeping the center of combustion at a constant value is formulated as an optimization problem with an equality constraint. A combination of feedback control and extremum seeking is used to solve this optimization problem online. The necessity to separate the different time scales is discussed and a structure is proposed that facilitates this separation for this specific example. The proposed method is validated by experiments on a test bench.

Analysis of semi-physical neural network structure for model-based ignition timing control of multi-fuel SI engines

This research investigates the use of a semi-physical neural network for combustion phasing control of a multi-fuel spark ignition engine. The influence of model structure and training data set composition are each analysed for their influence on combustion phasing control accuracy under steady-state and transient engine operating conditions. The model structure developed for this research utilises both fuel sensitive and combustion related physical models as inputs, with an aim to minimise neural network size and increase its generalisation capability. Optimisation of the network structure is also studied to evaluate overall robustness and ensure control stability. Real-time engine test results show satisfactory combustion phasing control performance with multiple fuels for both steady state and transient conditions. Moreover, demonstration of the differences of controller performance brought by the steady state and transient training data samples will be also provided.

Adaptive Control of a Recompression Four-Cylinder HCCI Engine

An adaptive controller is presented for the control of combustion phasing in a multicylinder homogeneous charge compression ignition engine. Adaptive parameter estimation is used to modify a model-based feedforward controller for each cylinder’s start of injection (SOI) timing in an effort to mitigate model errors and increase the feedforward control accuracy. In-cylinder pressure measurements are used to calculate combustion phasing, which is compared with the prediction of an online nonlinear engine model to drive the parameter estimation that adapts the feedforward controller. It is demonstrated through experiments that the adaptive parameter can reduce the parameterization effort by allowing the model to adapt and match the response of each cylinder. It is also shown that the adaptive feedforward control is more accurate in the sense that load transitions can be achieved with less correction from the feedback controller. Overall, an average reduction of 41% in the absolute value of the SOI feedback component at steady state is achieved.

Multidimensional modeling of the effect of Exhaust Gas Recirculation (EGR) on exergy terms in an HCCI engine fueled with a mixture of natural gas and diesel

One of the most important issues in HCCI engines is auto-ignition timing control. EGR introduction into intake charge can be a method to control combustion phasing and its duration. In the current study, a FORTRAN-based code which includes 10 species (O2, N2, H2O, CO2, CO, H2, OH, O, N, NO) associated with combustion products was employed to study the exergy analysis in a dual fuel (natural gas+diesel) HCCI engine at four EGR (exhaust gas recirculation) mass fractions (0%, 10%, 20%, and 30%) while the diesel fuel amount was held constant. In order to achieve this task, a 3-D CFD code was employed to model the energy balance during a closed cycle of running engine simulation. Moreover, an efficient Extend Coherent Flame Model-Three Zone model (ECFM-3Z) method was employed to analyze the combustion process. With crank positions at different EGR mass fractions, the exergy terms were identified and calculated separately. It was found that as EGR mass fraction increased from 0% to 30% (in 10% increment steps), exergy efficiency decreased from 48.9% to 28.7%. Furthermore, with the change in EGR mass fraction, the cumulative heat loss exergy decreased from 10.1% to 5.64% of mixture fuels chemical exergy.

An Alternative Method to MFB50 for Combustion Phase Detection and Control in Common Rail Diesel Engines

Although injection timing does not change at every cycle in compression ignition engines, the variations in combustion phase may occur. The variations in combustion phase are directly related to emission dispersion, torque variation, and fuel economy; therefore, the variations should be minimized by combustion phase detection and control. In this study, we propose a novel combustion indicator: location of 20% of initial heat release after the peak (IHRap20) that is an alternative to MFB50 to detect and control combustion phase in real time. IHRap20 is extracted from IHR, which is a simplified heat release model derived by the product of in-cylinder volume and the gradient of difference pressure between firing pressure and motoring pressure. IHRap20 is confirmed with engine experiment that it is highly correlated to MFB50 with RMSE of 0.2790° crank angle and R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 0.9873 under various operating conditions such as injection timing, mass air flow, boost pressure, and rail pressure changes. In addition, IHRap20 is able to detect combustion phase in real time with fewer number of in-cylinder pressure data and computational load compared to MFB50. Furthermore, IHRap20 is more robust to in-cylinder pressure sensor noise than MFB50. Consequently, IHRap20 is promising for real-time combustion phase detection.

Progress and recent trends in reactivity-controlled compression ignition engines

Low-temperature combustion is an emerging engine technology that has the ability to yield low NOx and soot emissions while maintaining high fuel efficiency. Low-temperature combustion strategies include homogeneous charge compression ignition, premixed charge compression ignition, reactivity-controlled compression ignition and partially premixed combustion. These low-temperature combustion strategies use early fuel injections to allow sufficient time for air–fuel mixing before combustion. According to the literature, some low-temperature combustion strategies are not promising for future automotive and power generation applications due to difficulties in controlling the heat release rate and the lack of a combustion phasing control mechanism. To mitigate these problems, the reactivity-controlled compression ignition combustion concept was introduced. Reactivity-controlled compression ignition is a dual-fuel partially premixed combustion concept, which uses port fuel injection of a low-reactivity fuel (e.g. gasoline, natural gas and alcohol fuels) and direct injection of a high-reactivity fuel (e.g. diesel and biodiesel) with blending inside the combustion chamber to increase the combustion duration and to provide phasing control. Combustion phasing is controlled by the relative ratios of the two fuels, and the combustion duration is controlled by spatial stratification between the two fuels. This article begins by an overview of the different low-temperature combustion strategies and demonstrates some advantages of reactivity-controlled compression ignition, over homogeneous charge compression ignition and premixed charge compression ignition combustion strategies in regard to fuel flexibility and combustion controllability. A comprehensive review of recent research on various aspects of reactivity-controlled compression ignition and comparisons of thermal efficiency and pollutant emissions over conventional diesel combustion is also presented. This article presents the significance of reactivity-controlled compression ignition strategy as a promising solution for future automotive engines and discusses future research directions.

Numerical investigation of spontaneous flame propagation under RCCI conditions

This paper presents results from one and two-dimensional direct numerical simulations under Reactivity Controlled Compression Ignition (RCCI) conditions of a primary reference fuel (PRF) mixture consisting of n-heptane and iso-octane. RCCI uses in-cylinder blending of two fuels with different autoignition characteristics to control combustion phasing and the rate of heat release. These simulations employ an improved model of compression heating through mass source/sink terms developed in a previous work by Bhagatwala et al. (2014), which incorporates feedback from the flow to follow a predetermined experimental pressure trace. Two-dimensional simulations explored parametric variations with respect to temperature stratification, pressure profiles and n-heptane concentration. Statistics derived from analysis of diffusion/reaction balances locally normal to the flame surface were used to elucidate combustion characteristics for the different cases. Both deflagration and spontaneous ignition fronts were observed to co-exist, however it was found that higher n-heptane concentration provided a greater degree of flame propagation, whereas lower n-heptane concentration (higher fraction of iso-octane) resulted in more spontaneous ignition fronts. A significant finding was that simulations initialized with a uniform initial temperature and a stratified n-heptane concentration field, resulted in a large fraction of combustion occurring through flame propagation. It was also found that the proportion of spontaneous ignition fronts increased at higher pressures due to shorter ignition delay when other factors were held constant. For the same pressure and fuel concentration, the contribution of flame propagation to the overall combustion was found to depend on the level of thermal stratification, with higher initial temperature gradients resulting in more deflagration and lower gradients generating more ignition fronts. Statistics of ignition delay are computed to assess the Zel’dovich (1980) theory for the mode of combustion propagation based on ignition delay gradients.

Experimental study on fuel economies and emissions of direct-injection premixed combustion engine fueled with gasoline/diesel blends

The effects of gasoline/diesel blended fuel composed of diesel fuel with gasoline as additives in volume basis, on combustion, fuel economies and exhaust emissions were experimentally investigated. Tests were carried out based on a turbocharged Common-rail Direct Injection engine at a constant engine speed of 1800r/min and different loads of 3.2bar, 5.1bar Indicated Mean Effective Pressure. Additionally, the effect of combustion phasing and Exhaust Gas Recirculation were evaluated experimentally for various fuels. The results indicated that with the fraction of gasoline increasing in blends, the ignition delay was prolonged and the combustion phasing was retarded with the common injection timing. This led to a significant increase of premixed burning phase, which was in favor of smoke reduction; although, too much gasoline might be adverse to fuel consumption. An optimum combustion phasing was identified, leading to a higher thermal efficiency and better premixed combustion with blended fuels. A combined application of Exhaust Gas Recirculation and blended fuel with a high gasoline fraction was confirmed effective in reducing the oxides of nitrogen and smoke emissions simultaneously at the optimum combustion phasing without giving significant penalty of fuel consumption. A compound combustion mode with its emission lower than the conventional Compression Ignition engines, and efficiency higher than the typical Spark Ignition engines, could be achieved with a cooperative control of Exhaust Gas Recirculation and combustion phasing of the gasoline/diesel blended fuels.

Modeling of combustion phasing of a reactivity-controlled compression ignition engine for control applications

Reactivity-controlled compression ignition (RCCI) is a promising combustion strategy to achieve near-zero NOx and soot emissions and diesel-like efficiencies. Model-based control of RCCI combustion phasing requires a computationally efficient combustion model that encompasses factors such as injection timings, fuel blend composition, and reactivity. In this work, physics-based models are developed to predict the onset of auto-ignition in RCCI and to estimate the burn duration based on an approximation of the spontaneous ignition front speed. A mean value control-oriented model of RCCI is then developed by combining the auto-ignition model, the burn duration model, and a Wiebe function to predict combustion phasing. The control-oriented model is parameterized and validated using simulation data from an experimentally validated, detailed computational fluid dynamics combustion model developed using the KIVA-3V code. The validation results show that the control-oriented model can predict the start of combustion, burn duration, and crank angle of 50% burnt fuel with an average error of less than 2 crank angle degrees. Thus, the control-oriented model demonstrates sufficient accuracy in predicting RCCI combustion phasing for control applications. The control-oriented model is an integral part of designing a model-based controller, which in the case of RCCI is of paramount importance due to various attributes concerning combustion, particularly for transient engine operation.

Effects of injection pressure, exhaust gas recirculation and intake pressure on the cycle-to-cycle variations of HCCI combustion

Combustion in HCCI engines is a controlled auto ignition process of well-mixed fuel, air and residual gas. Since the ignition of HCCI combustion is completely controlled by chemical kinetics, and is directly affected by the fuel composition, equivalence ratio, and thermodynamic state of the mixture, there is no direct control on the start of combustion process. Therefore, HCCI combustion is easy to become unstable, especially at lower and higher engine loads. In this study, cycle-to-cycle variations of an HCCI combustion engine fuelled with diesel were investigated on a modified single-cylinder engine. The experiments were conducted at different injection pressures, EGR rates, and intake pressures at constant engine speed of 1500 rpm. One hundred consecutive combustion cycles for each test conditions at steady state operation were recorded. Consequently, cycle-to-cycle variations of the main combustion parameters and performance parameters were analyzed. Coefficients of variation (COV) of every parameter were calculated to evaluate the cycle-to-cycle variations of HCCI combustion. This provides basis for closed loop control of diesel HCCI combustion phasing.

Numerical investigation on the effect of reactivity gradient in an RCCI engine fueled with gasoline and diesel

The reactivity controlled compression ignition (RCCI), which belongs to dual fuel mode (DFM) combustion has been considered as a promising way to achieve high fuel conversion efficiency and low emissions. By this strategy, a fuel reactivity gradient is formed in the combustion chamber which offers the probability of controlling combustion phasing. In this study, the role of fuel reactivity gradient was examined numerically by comparing a DFM (i.e., RCCI) combustion with other hypothetical cases under one specific load condition. Firstly, a chemical reaction mechanism was developed aiming at a modelling study on dual fuel and blend fuel combustion in internal combustion (IC) engines fueled by gasoline/diesel and gasoline/biodiesel. Ignition delays were validated for 100% diesel, 100% gasoline and 100% biodiesel under 102 conditions in total. Subsequently, the validated reaction mechanism which consists of 107 species and 425 reactions was implemented in coupled KIVA4-CHEMKIN code. Three dimensional validations were further conducted under 3 conditions including pure diesel combustion, and gasoline/diesel DFM combustion with both single and double injection strategies in the engine. To investigate the fuel reactivity gradient, the gasoline/diesel DFM combustion with single injection was compared with other three hypothetical cases, one of which was DFM without fuel reactivity gradient, two were the blend fuel mode but with different start of injection (SOI) timings. The results showed that the fuel reactivity gradient could retard the ignition timing, reduce heat release rate, and ease peak pressure rise rate. In addition, low levels of NOx and soot emissions were observed for the DFM combustion. The gasoline/biodiesel reaction mechanism will be employed in future work.

Combustion Phase Control of SI Gasoline Engines Using Hypothesis Test

In order to maximize the performance of internal combustion engines, combustion phase is usually controlled to track its optimal setpoint. In this paper, as one of combustion phase indicators, location of peak pressure (LPP) is employed for combustion phase control. In the statistic point of view, hypothesis test is utilized to check the distribution of LPP, then a decision block is designed based on the statistics of LPP. Using the mean of LPP calculated by the presented hypothesis test algorithm, a simple steady model based controller is synthesized, which regards spark advance as system input. Finally, the proposed strategy is verified by the experiment test on a spark ignition gasoline engine.

Effect of hydrogen peroxide addition to methane fueled homogeneous charge compression ignition engines through numerical simulations

The effect of the direct injection of hydrogen peroxide into a port-injected methane fueled homogeneous charge compression ignition engine was investigated numerically. The injection of aqueous hydrogen peroxide was implemented as a means of combustion phasing control. A single-cylinder homogeneous charge compression ignition engine (2.43 L Caterpillar) was modeled using the Cantera 2.0 flame code toolkit, the GRI-Mech 3.0 chemical reaction mechanism, and a single-zone slider-crank engine model. Start of injection timing and the amount of injected hydrogen peroxide were manipulated to achieve desired combustion phasing under a wide range of intake temperatures. As the concentration of hydrogen peroxide is increased, the combustion phasing is advanced up to 22° for the conditions investigated in this study. This advancing effect is most pronounced at small concentrations (&lt;10 g H2O2/kg CH4) and early injection timings (start of injection &lt; 25° before top dead center). The model suggests hydrogen peroxide can be introduced as a means of combustion phasing control while maintaining the low emissions and peak in-cylinder pressures inherent in homogeneous charge compression ignition engines.

Investigation of the sources of combustion instability in low-temperature combustion engines using response surface models

In the search for more efficient and cleaner engines, low-temperature combustion engines have emerged with the potential to simultaneously increase engine efficiency and reduce nitrogen oxides and soot emissions. Although promising, low-temperature combustion engines have not been widely implemented due to difficulties controlling combustion phasing, combustion duration, and cycle-to-cycle variation. This article develops a methodology using detailed computational fluid dynamics simulations to investigate cycle-to-cycle instability of homogeneous charge compression ignition and reactivity-controlled compression ignition engines. Using computational fluid dynamics modeling, a large design of experiment is performed with small perturbations to the intake and fueling conditions. A response surface model is then fit to the design of experiment results to predict the combustion characteristics and exercised to determine the main sources of cycle-to-cycle variation. As expected, the results show that reactivity-controlled compression ignition and homogeneous charge compression ignition have significantly more variation than conventional diesel combustion. Reactivity-controlled compression ignition combustion phasing (CA50—crank angle when 50% of fuel is burned) is most sensitive to variations in diesel fuel mass, level of exhaust gas recirculation, and charge gas temperature. The peak pressure rise rate of reactivity-controlled compression ignition combustion is most sensitive to variations in gasoline fuel mass. The sources of variation for homogeneous charge compression ignition are similar to those of reactivity-controlled compression ignition combustion; however, trapped gas pressure and cylinder liner temperature become significant factors. Because of the late combustion phasing required for homogeneous charge compression ignition to maintain acceptable pressure rise rate, its cycle-to-cycle variation was found to be higher than that of reactivity-controlled compression ignition combustion for the same input variations.

Controlling the Power Output and Combustion Phasing in an Homogeneous Charge Compression Ignition Engine

In the development of Homogeneous Charge Compression Ignition (HCCI) engines, simultaneous control of combustion phasing and power output has been a major challenge. In this study, a new strategy is developed to control the engine power output and combustion phasing at any desired operating condition. A single zone thermodynamic model coupled to a full kinetic mechanism of Primary Reference Fuels (PRFs) is developed to predict characteristic parameters such as; Start of Combustion (SOC) and Indicated Mean Effective Pressure (IMEP) and also thermodynamic constant parameters for processes through an HCCI engine cycle. A dynamic interactive control model has been developed for the entire cycle of a HCCI engine to predict combustion phasing and IMEP.The results derived from the developed model are validated against experimental data for a single cylinder Ricardo engine. A two input two output controller is then designed to track crank angle at which 50% of in cylinder fuel mass is burned (CA50) and IMEP by adjusting the input data. In this study two control models are presented; open loop and closed loop. Performance of the controller is tested on a physical HCCI engine model to evaluate the tracking performance and disturbance rejection properties. Results indicate that the designed controller is capable to accurately tracking both CA50 and IMEP while rejecting the disturbances from variations in the engine speed and the intake manifold temperature. doi: 10.5829/idosi.ije.2014.27.11b.14

Closed-loop diesel engine combustion phasing control based on crankshaft torque measurements

Methods for closed-loop combustion phasing control in a diesel engine, based on measurements of crankshaft torque, are developed and evaluated. A model-based method for estimation of cylinder individual torque contributions from the crankshaft torque measurements is explained and a novel approach for identification of crankshaft dynamics is proposed. The use of the combustion net torque concept for combustion phasing estimation in the torque domain is also described. Two different control schemes, one for individual cylinder control and one for average cylinder control, are studied. The proposed methods are experimentally evaluated using a light-duty diesel engine equipped with a crankshaft integrated torque sensor. The results indicate that it is possible to estimate and control on a cylinder individual basis using the measurements from the crankshaft torque sensor. Combustion phasing is estimated with bias levels of less than 0.5 crank angle degrees (CAD) and cycle-to-cycle standard deviations of less than 0.7 CAD for all cylinders and the implemented combustion phasing controllers manage to accurately counteract disturbances in both fuel injection timing and EGR fraction.

Homogeneous charge compression ignition (HCCI) combustion: Mixture preparation and control strategies in diesel engines

Abstract At present achieving fuel economy and reducing emissions are the two main targets set by the automotive industries. Homogeneous charge compression ignition (HCCI) technology is believed to be a promising one to be applied in both spark ignition (SI) and compression ignition (CI) engines in the near future. However, some challenges such as compromise combustion phase control, controlled auto-ignition, operating range, homogeneous charge preparation, cold start and emissions of unburned hydro carbon (UHC), and carbon monoxide (CO) need to be overcome for successful operation of HCCI engine. Extensive research on HCCI combustion with a homogeneous fuel–air mixture preparation is going on throughout the world. This paper reviews the strategies of different external and in-cylinder mixture preparation methods which were adopted and proposed in the recent years. The different strategies of controlled auto-ignition by HCCI combustion are also discussed in this paper.

Experimental and Numerical Study of Jet Controlled Compression Ignition on Combustion Phasing Control in Diesel Premixed Compression Ignition Systems

In order to directly control the premixed combustion phasing, a Jet Controlled Compression Ignition (JCCI) for diesel premixed compression ignition systems is investigated. Experiments were conducted on a single cylinder natural aspirated diesel engine without EGR at 3000 rpm. Numerical models were validated by load sweep experiments at fixed spark timing. Detailed combustion characteristics were analyzed based on the BMEP of 2.18 bar. The simulation results showed that the high temperature jets of reacting active radical species issued from the ignition chamber played an important role on the onset of combustion in the JCCI system. The combustion of diesel pre-mixtures was initiated rapidly by the combustion products issued from the ignition chamber. Moreover, the flame propagation was not obvious, similar to that in Pre-mixed Charge Compression Ignition (PCCI). Consequently, spark timing sweep experiments were conducted. The results showed a good linear relationship between spark timing in the ignition chamber and CA10 and CA50, which indicated the ability for direct combustion phasing control in diesel PCCI. The NOx and soot emissions gradually changed with the decrease of spark advance angle. The maximum reduction of NOx and soot were both over 90%, and HC and CO emissions were increased.

Grey-box modeling of HCCI engines

Homogenous Charge Compression Ignition (HCCI) holds promise to increase indicated thermal efficiency and reduce Nitrogen Oxides (NOx) and Particulate Matter (PM) emissions from internal combustion engines. Lack of a direct means to initiate the combustion and high levels of Total Hydrocarbon (THC) and Carbon Monoxide (CO) emissions are major drawbacks associated with HCCI engines. Control of combustion phasing for optimum indicated thermal efficiency and minimizing emissions are vital for putting HCCI engines into practice. One major challenge is to develop accurate models for understanding engine performance, as those models can run real-time for HCCI control. This paper develops the first computationally efficient grey-box model for predicting major HCCI engine variables. The grey-box model consists of a combination of physical models and three feed-forward artificial neural networks models to estimate six major HCCI variables including combustion phasing, load, exhaust gas temperature, THC, CO, and NOx emissions. The grey-box model is experimentally validated over a large range of HCCI engines operation including 309 steady state and transient test conditions. The validation results show that the grey-box model is able to predict the HCCI engine outputs with average relative errors less than 10%. Performance of the grey-box methodology is tested for two different HCCI engines and the verification results show that the developed six-output grey-box model can be successfully used for performance modeling of different HCCI engine applications.

An investigation of semiphysical artificial neural networks for multi-fuel combustion phasing control of spark ignition engines

The number of engine control actuators and potential fuel sources are constantly increasing to meet fuel economy targets and global energy demand. The increased engine control complexity resulting from new actuators and fuels motivates the use of model-based control methodologies over map-based empirical approaches. Purely physics-based control techniques have the potential to decrease calibration burdens but must be complex to represent nonlinear engine behavior with low computational requirements. Artificial neural networks are recognized as powerful tools for modeling systems which exhibit nonlinear relationships, but they lack physical significance. Combining these two techniques to produce semiphysical artificial neural network models which provide acceptable accuracy while minimizing the artificial neural network size, the calibration effort and the computational intensity is the focus of this research. To minimize the size of the neural network, sensitivity analyses are carried out on the critical inputs and the minimum number of required neurons. The most critical physical parameters are selected as follows: the laminar flame speed; the turbulence intensity; the total in-cylinder mass. The control algorithm derivation is described, and the process validated in real time using an engine dynamometer. The real-time experimental results demonstrate that the semiphysical artificial neural network approach can produce accurate ignition timing control for both gasoline and E85. Robustness of the semiphysical neural network approach is also discussed on the basis of the real-time experimental results.