Peak Firing Pressure Research Articles

Effective measures to improve thermal efficiency of medium-sized diesel engine in practical application: Energy-exergy analysis and test verification

As the fourth stage of China’s fuel consumption limits for heavy commercial approaches, engine manufacturers are facing huge challenges. Here, the impact of different strategies on brake thermal efficiency (BTE) was studied through experiments and simulations, and the main energy loss items were obtained based on energy and exergy analysis. According to experimental results, the removal of exhaust gas recirculation (EGR) mainly reduced exhaust losses, resulting in a 0.5% increase in BTE at 1200 r/min. Turbocharger scheme 2, with a high flow rate and high efficiency, was beneficial in reducing pumping losses. Owing to consistent brake power, simultaneously increasing the compression ratio and peak firing pressure can reduce the exhaust losses and combustion irreversibility. When fuel injection quantity was constant, the use of high flow injectors could advance CA50, thereby increasing output power and reducing exhaust losses. Finally, the actual development of the new engine was completed, and the test results showed that the maximum BTE reached 46.9%, and CO and soot emissions were reduced by 74.2% and 78.3%, respectively. Therefore, for medium-sized diesel engines, adopting the non-EGR route, using high flow turbochargers and injectors, and increasing compression ratio can effectively improve BTE and reduce carbon emissions.

Engine combustion modeling method based on hybrid drive

Accurate and comprehensive reconstruction of in-cylinder combustion process is essential for timely monitoring of engine combustion state. This article developed a method based on the zero-dimensional (0-D) physical model integrated with big data. The traditional 0-D prediction model based on cumulative fuel mass is improved, the factor of in-cylinder temperature is introduced to adjust the heat release rate, which solves the problem of difficulty in calibrating the heat release rate. Then, convolutional neural network-gated recurrent unit (CNN-GRU), as a deep neural network, including a special convolutional layer and a gated recurrent unit (GRU) neural network is designed for the parameters to be calibrated in the model. The 0-D predictive combustion model is constructed by combining the physical model with CNN-GRU, the combustion process is simplified and reconstructed. The fitting results show that the 0-D physical model based on improved cumulative fuel mass approach is an effective method to reflect the heat release law. Under non-calibration conditions, the root mean square error (RMSE) value of peak firing pressure (PFP) based on CNN-GRU prediction model is 0.5862. The prediction model is a promising method to realize online fitting and optimization of combustion process.

Advanced model-based closed-loop combustion control strategies with combustion rate shaping

Combustion rate shaping (CRS) is an advanced closed-loop concept which controls the crank-angle resolved combustion trace by adapting the fuel injection profile. The thermodynamic potential of this concept to enable real-time combustion control independent of fuel property variations, injector drift, cylinder tolerances, or changing air-path boundary conditions has already been demonstrated. The highest benefit of this control concept is achieved when it is directly applied on the engine control unit (ECU) in combination with an in-cylinder pressure measurement. This enables online optimization and adaption of the fuel- and air-path settings to the fuel used during vehicle operation. Therefore, the development of a CRS concept with real-time capability has been the main focus so far. To ensure a robust online real-time combustion control, a key development step was the identification of control variables that describe the entire combustion process and only minimally influence each other. For this purpose, the combustion phasing, the combustion gradient and the indicated mean effective pressure have been determined as parameters for the feedback control. However, the stringent requirements for higher efficiencies, emission robustness and combustion noise necessitate the extension of the CRS control concept. Therefore, in this work, the CRS control concept is extended with the aim of realizing a combustion with constant volume pressure increase to the peak firing pressure limit to achieve highest efficiency. In addition, intelligent control of the fuel injection profile is to be used to achieve a combustion temperature for lowest possible NOx raw emissions and a robust combustion noise excitation limitation. The optimized control strategy is implemented on a heavy-duty single cylinder engine test bench using a Rapid Control Prototyping (RCP) system, and the control performance is demonstrated.

A New Simulation-Based Methodology to Improve Medium-Speed Diesel Engines BSFC/NOx Tradeoff With an Optimized Air Charging System

Abstract This paper aims at introducing an original, simulation based, methodology to optimize air charging system of a medium speed engine in order to improve fuel consumption/NOx tradeoff, over a given load profile. A preliminary study is performed on an engine originally equipped with fixed geometry turbocharger (TC) matched at full load. It shows that improving the TC efficiency has a positive impact at matching point but an adverse effect at lower loads. Therefore, matching the TC at part load is more promising when the whole engine operating range is considered. However, this requires using a relief system to avoid unacceptable peak firing pressure (PFP) at full load, and may alter regulated NOx emission. A new, original methodology is then proposed. Using an advanced existing algorithm, it allows for simultaneous optimization of injection timing, main TC matching and relief system design. The objective is to minimize fuel consumption averaged over several operating points (corresponding to actual load profile). At the same time, NOx emission, evaluated on regulatory cycle, is kept below a given limit and others reliability constrains are fulfilled. The methodology is assessed with several case studies: • First, various relief systems (blow-off valve, waste gate (WG) and parallel sequential turbocharger (PTC)) are compared on a given load profile. • Then, the dimensioning of a TC + WG system is performed for two different load profiles. In both cases, the proposed methodology leads to a charging system design customized for a given user profile, which enables a significant fuel consumption reduction.

In-cylinder pressure reconstruction from engine block vibrations via a branched convolutional neural network

We introduce a novel approach to reconstructing the in-cylinder pressure trace from vibration signals recorded with common knock sensors. The proposed methodology is purely data-driven and employs a convolutional neural network that has two distinct branches. Each branch is allowed to learn individual aspects of the mapping process, with boundary conditions within the model architecture set to incentivize the individual branches to learn low-frequency and high-frequency contents of the pressure trace.The reconstruction achieves calculated Pearson coefficients and coefficients of determination above 0.99 for all investigated datasets and a Mean Absolute Error of under 2.7 bar across all processed cycles. Furthermore, peak firing pressure and peak pressure position were extracted from the reconstructed cycles. Hereby, the method achieves Mean Absolute Error values of under 4.3 bar for peak firing pressure and under 1°crank angle for peak pressure position across all processed datasets, despite them not explicitly being targets of the underlying task.Deeper investigation of the results shows that combustion anomalies such as knocking do not negatively influence model fit. Moreover, model limitations were identified for high-pressure cycles and cycles exemplifying rather slow combustion.

Estimation of Combustion Parameters from Engine Vibrations Based on Discrete Wavelet Transform and Gradient Boosting

An optimal control of the combustion process of an engine ensures lower emissions and fuel consumption plus high efficiencies. Combustion parameters such as the peak firing pressure (PFP) and the crank angle (CA) corresponding to 50% of mass fraction burned (MFB50) are essential for a closed-loop control strategy. These parameters are based on the measured in-cylinder pressure that is typically gained by intrusive pressure sensors (PSs). These are costly and their durability is uncertain. To overcome these issues, the potential of using a virtual sensor based on the vibration signals acquired by a knock sensor (KS) for control of the combustion process is investigated. The present work introduces a data-driven approach where a signal-processing technique, designated as discrete wavelet transform (DWT), will be used as the preprocessing step for extracting informative features to perform regression tasks of the selected combustion parameters with extreme gradient boosting (XGBoost) regression models. The presented methodology will be applied to data from two different spark-ignited, single cylinder gas engines. Finally, an analysis is obtained where the important features based on the model’s decisions are identified.

Influence of Combustion Duration on the Performance and Emission Characteristics of a Spark-Ignition Engine Fueled with Pure Methanol and Ethanol.

In this research, we estimated and summarized the effects of combustion duration on the performance and emission characteristics of a spark-ignition engine using pure methanol and ethanol as fuels, which have not been previously presented. From the results, we demonstrated that an increase in combustion duration causes a decrease in peak firing temperature and peak firing pressure and an increase in trapped residual gas. The level of trapped residual gas when using ethanol as fuel is higher than that of methanol fuel. The indicated mean effective pressure (IMEP) and brake mean effective pressure (BMEP) increase to maximum values and then decrease with increasing combustion duration, while the brake specific fuel consumption (BSFC) reaches a minimum value and then increases. The optimal BSFC improved to 33.31% when the engine used ethanol fuel instead of methanol. The increase in combustion duration helps to reduce NOx and HC emissions, but an increase in CO emissions is observed.

Use of thermodynamic models for compression ratio and peak firing pressure optimization in heavy-duty diesel engine

European Union Commission declared 30% CO2 reduction target for 2019 report-out for heavy-duty vehicles. Nowadays, the main focus of automotive manufacturers is reducing CO2 emissions. To ensure 30% CO2 emission reduction, companies are examining the effect of different fuel economy contributors. Developing prototype diesel engines and performing tests for different conceptual studies are both expensive and complicated conditions. As a result, OEMs should employ virtual tools with an enhancing trend. In this paper, the fuel economy improvement effects of increasing the compression ratio and maximum in-cylinder pressure limitation in the 12.7L heavy-duty diesel engine are examined using a thermodynamic model rather than actual dynamometer tests. Initially, the generated thermodynamic model is correlated with dynamometer test data. A predictive combustion model is used. NOx emission prediction correlation is also performed. Then, the most vital operating points representing VECTO and on-road fuel economy cycles are detected. At these critical operating points, the thermodynamic model is run with varied calibration parameters such as fuel injection quantity & timing, boost pressure & air mass flow set points. Thermodynamic model outputs are used for the Gaussian Process Model generation. A multi-objective optimization methodology is utilized to thoroughly examine the fuel consumption and NOx emission trade-off trends for various peak firing pressure hardware limit and compression ratios scenarios. It is proven that since the fuel residency of part load points is more critical than full load points in the VECTO cycle and long haul vehicles, the CO2 reduction potential of increasing compression ratio is observed to be comparatively lower concerning increasing peak firing pressure limit. The methodology can be utilized for performing fast and accurate fuel economy benefits examination of different technologies or concepts in a virtual platform resulting in a significant reduction in the number of actual dynamometer tests.

Effect of peak firing pressure constraint on thermal efficiency of a Sabathe-Miller engine

How to Improve the thermal efficiency of internal combustion engine is an eternal topic since it is directly related to energy consumption and pollution emissions. Among lots of technologies applied on heavy duty diesel engine, Miller cycle which increases the effective expansion ratio in relation to the compression is proved to be a good choice to balance engine performance with fuel economy and CO2/NOx/smoke emissions. However, limitation of peak firing pressure (PFP) will restrict the intake pressure or compression ratio of miller engines which in turn influence the thermal efficiency, and their in-depth trade-off relationship is not clear yet. Using the engine cycle simulation, this paper explores the most reasonable cylinder pressure waveform limited by PFP and found there exists an optimized pressure ratio values which slightly affected by other operating conditions for Sabathe-Miller cycle engine. Thereafter, effects of PFP limit on the performance of a large single cylinder engine were investigated considering the effect of engine load, miller degree, equivalence ratio as well as engine speed. It is found that under full load condition, the maximum brake thermal efficiency occurs when pressure ratio (PR) is about 1.2, and PFP constraint plays a dominant role on brake efficiency and could contribute more than 4.0% efficiency by increasing PFP constraint from 250bar to 350bar. Compared with full load condition, the brake thermal efficiency increases 4.6% and 6.3% respectively under fuel-rich (extremely high CR) and lean-burn (low heat loss) half load conditions. Meanwhile, miller degree was optimized for Sabathe-Miller cycle, and it plays a key role on reducing combustion temperature instead of increasing thermal efficiency compared with effect of PFP constraint.

Technologies integration to achieve brake thermal efficiency beyond 55% for HD diesel engines

This study focuses on the technologies integration to aim about 60% indicated thermal efficiency (ITE) with a single-cylinder HD diesel engine, roughly equivalent to 55% brake thermal efficiency (BTE) with multiple-cylinder engines. A new thermodynamic cycle concept and a new heat insulation structure were discussed as the key integrated technologies. Otto cycle is the best thermodynamic cycle for ideal thermal efficiency. However, significant increase in heat release rate around top dead center results in higher cooling loss and sometimes in deterioration of late combustion under a higher compression ratio without any improvement in ITE. The newly proposed cycle is the hybrid of isobaric cycle and following steep pressure increase up to peak firing pressure (PFP) constraint from the timing when in-cylinder volume change rate becomes significant, which suppresses the average gas temperature. For further cooling loss reduction, the new in-cylinder wall insulating concept was investigated. The in-cylinder insulating effect was much significant by applying not only on the piston crown but also on the cooling side of piston. Although the test engine hasn’t been optimized yet, ITE was almost reached at about 60% by means of the multiple-injector concept with compression ratio of 23.5:1.

Least life analysis of diesel locomotive crankshaft

An analysis of the diesel locomotive crankshaft failure is presented in this paper. The crankshaft of diesel locomotives is badly affected by the peak firing pressure and cooling water temperature. The main aim of this study work was to investigate the finite element analysis on a forged steel crankshaft of diesel locomotive using ANSYS software and to suggest some novel simulation strategy that is based on the size and design consideration of the crankshaft fillet radius. The investigation included the following testing techniques and experimental process: selection of the crankshaft for investigation, visual examination, non-destructive testing of the crankshaft, failure analysis, 3D modeling of the crankshaft and finite element analysis. In this paper, a novel approach was developed in which the main crankshaft under static structural condition was analyzed by varying its fillet radius. The crankshaft was impersonated into CAM software SOLIDWORKS and after 3D modeling, its finite element analysis was performed in ANSYS software. The crankshaft was subjected to peak firing pressure and its least fatigue life was analyzed by varying the fillet radius of the crankshaft in the step of 0.5″. The analysis result shows the significant improvement in the least life cycles of the locomotive crankshaft and it was found to be 1205.9 cycles with 5/8″ fillet radius as compared to 571.54 cycles with original fillet radius size of 3/8″. The total heat flow producing thermal and surface cracks on the crankpin and main journal bearing was found to be low in the crankshaft resulting in a substantial improvement in the overall age of the locomotive crankshaft.

Holistic Engine and EAT Development of Low NO <sub>X</sub> and CO <sub>2</sub> Concepts for HD Diesel Engine Applications

<div class="section abstract"><div class="htmlview paragraph">The latest legislative tendencies for on-highway heavy duty vehicles in the United States such as the feasibility assessment of low NO<sub>X</sub> standards of CARB or EPA’s memorandum forecast further tightening of the NO<sub>X</sub> emissions limits. In addition, the GHG Phase 2 legislation and also phased-in regulations in the EU enforce a continuous reduction in CO<sub>2</sub> emissions resp. fuel consumption. In order to meet such low NO<sub>X</sub> emission limits, a rapid heat-up of the exhaust after-treatment system (EATS) is inevitable. However, the required thermal management results in increased fuel consumption, i.e. CO<sub>2</sub> emissions as shown in numerous previous works also by the authors. A NO<sub>X</sub>-CO<sub>2</sub> trade-off for cumulative cycle emissions can be observed, which can be optimized by using more advance technologies on the engine and/or on the EATS side.</div><div class="htmlview paragraph">In the present study a systematic investigation is carried out by means of model-based holistic approach targeting the definition of a high efficiency engine layout and optimal thermal management calibration. First, the potentials of combustion process optimization (compression ratio, peak firing pressure) and of turbocharger efficiency increase are quantified aiming engine efficiency increase. Afterwards, using holistic engine and EAT concept development approach, conventional and advanced EATS layouts are tested. The advanced EATS layout consist of a close-coupled dual-stage SCR system. In order to explore the benefits of each layouts, the engine heat-up calibrations are varied and the resulting, cumulative NO<sub>X</sub>-CO<sub>2</sub> emissions of the investigated cycle are compared and evaluated. Multiple improvement measures for both engine and EAT system are discussed and an outlook of future powertrain concepts is given.</div></div>

The effects of bore-stroke ratio on effective release energy, residual gas, peak pressure rise and combustion duration of a V-twin engine

In our continual effort to develop an improved performance of a V-twin engine, we investigated the effective release energy, residual gas, peak pressure rise and combustion duration using experimental and simulation approaches. Through combined experimental and simulation methods, the results of the research show that the peak firing pressure rise, combustion duration, and effective release energy were strongly dependent on bore-stroke ratio, while the residual gas was less dependent on bore-stroke ratio. The increase of the bore-stroke ratio led to decrease residual gas ratio, effectively release energy, and increase ignition timing, combustion duration, and volume efficiency. At the bore-stroke ratio of 0.966, the peak firing pressure rise achieved its maximum value of 3.05 bar/deg. The HC and CO emissions were reduced but NOx was increased. At a bore-stroke ratio of 0.8, the maximum engine torque was improved by 7.68 % compared to the reference bore-stroke ratio of 1.06. The engine emitted the least NOx at a 0.88 bore-stroke ratio.

Comparative Study of the Effective Release Energy, Residual Gas Fraction, and Emission Characteristics with Various Valve Port Diameter-Bore Ratios (VPD/B) of a Four-Stroke Spark Ignition Engine

In this research, the residual gas, peak firing pressure increase, and effective release energy were completely investigated. To obtain this target, the experimental system is installed with a dynamo system and a simulation model was setup. Through combined experimental and simulation methods, the drawbacks of the hardware optimization method were eliminated. The results of the research show that the valve port diameter-bore ratio (VPD/B) has a significant effect on the residual gas, peak firing pressure increase, and effective release energy of a four-stroke spark ignition engine. In this research, the engine was performed at 3000 rpm and full load condition. Following increased IPD/B ratio of 0.3–0.5. The intake port and exhaust port diameter has a contrary effect on engine volumetric efficiency, the residual gas ratio increase 27.3% with larger intake port and decrease 18.6% with larger exhaust port. The engine will perform optimal thermal efficiency when the trapped residual gas fraction ratio is from 13% to 14%. The maximum effective release energy was 0.45 kJ at 0.4 intake port-bore ratio, and 0.451 kJ at 0.35 exhaust port-bore ratio. The NOx emission increases until achieved a maximum value after that decrease even VPD/B was still increasing. With a VPD/B ratio of 0.35 to 0.4, the engine works without the misfiring.

Ultra-Lean Pre-Chamber Gasoline Engine for Future Hybrid Powertrains

<div class="section abstract"><div class="htmlview paragraph">Lean burn gasoline spark-ignition engines can support the reduction of CO<sub>2</sub> emissions for future hybrid passenger cars. Very high efficiencies and very low NOx raw emissions can be achieved, if relative air/fuel ratios λ of 2 and above can be reached. The biggest challenge here is to assure a reliable ignition process and to enhance the fuel oxidation in order to achieve a short burn duration and a good combustion stability.</div><div class="htmlview paragraph">This article aims at introducing an innovative combustion system fully optimized for ultra-lean operation and very high efficiency. Thereto, a new cylinder head concept has been realized with high peak firing pressure capability and with a low surface-to-volume ratio at high compression ratios. 1D and 3D simulations have been performed to optimize the compression ratio, charge motion and intake valve lift. Numerical calculations also supported the development of the ignition system. Stable ignition and fast flame propagation were achieved thanks to a centrally located active pre-chamber which allows to control the air/fuel ratio independently of the air/fuel ratio in the main combustion chamber.</div><div class="htmlview paragraph">Experimental investigations have then been performed with a single cylinder engine to demonstrate the capabilities of this new combustion system in a sweet spot operating point. A maximal indicated thermal efficiency of 47% was achieved at λ = 2 with optimized injection settings in the pre and main combustion chambers. The fuel efficiency could be maximized thanks to a fast and knock-free combustion process. Compared to the reference operation with stoichiometric air/fuel ratio, only a seventieth of the NOx raw emissions were measured (i. e. 50 ppm), and the particulate mass emissions were halved. The energy balance analysis points out that these promising results could be further improved by working on the reduction of the unburnt hydrocarbon emissions and by jointly optimizing the scavenging process.</div></div>

Comparison of Physics-Based, Semi-Empirical and Neural Network-Based Models for Model-Based Combustion Control in a 3.0 L Diesel Engine

A comparison of four different control-oriented models has been carried out in this paper for the simulation of the main combustion metrics in diesel engines, i.e., combustion phasing, peak firing pressure, and brake mean effective pressure. The aim of the investigation has been to understand the potential of each approach in view of their implementation in the engine control unit (ECU) for onboard combustion control applications. The four developed control-oriented models, namely the baseline physics-based model, the artificial neural network (ANN) physics-based model, the semi-empirical model, and direct ANN model, have been assessed and compared under steady-state conditions and over the Worldwide Harmonized Heavy-duty Transient Cycle (WHTC) for a Euro VI FPT F1C 3.0 L diesel engine. Moreover, a new procedure has been introduced for the selection of the input parameters. The direct ANN model has shown the best accuracy in the estimation of the combustion metrics under both steady-state/transient operating conditions, since the root mean square errors are of the order of 0.25/1.1 deg, 0.85/9.6 bar, and 0.071/0.7 bar for combustion phasing, peak firing pressure, and brake mean effective pressure, respectively. Moreover, it requires the least computational time, that is, less than 50 μs when the model is run on a rapid prototyping device. Therefore, it can be considered the best candidate for model-based combustion control applications.

Combustion System Design of a Genset Diesel Engine by Using DFSS Methodology

In this study, an optimum design for the combustion system of a genset diesel engine was conducted by using Design for Six Sigma (DFSS) methodology. As a result of this study, the best combination of design parameters to minimize the fuel consumption of the genset diesel engine was selected while meeting the requirements of NOx emission and peak firing pressure (PFP) limit. Compared to the initial design, the final design proposal has achieved 2.5 % and 1.6 % improvement in brake specific fuel consumption (BSFC) at switchable operating conditions, i.e., both 1500 and 1800 rpm. On the basis of this DFSS work, the design robustness was also enhanced. Hence, it is expected that the final design proposal would reduce the variability in fuel economy that could be caused by harsh environment and system aging. In this study, engine cycle simulation technique was employed to assess the effects of various design parameters on the performances of the genset diesel engine. The current optimum design work has considered four control factors such as turbocharger size, air temperature at charge air cooler (CAC) outlet, compression ratio, and fuel injection duration. Here, an L9 orthogonal array was used to efficiently choose the best design proposal among 81 design combinations (i.e., four independent control factors which individually have three different levels).

300 bar Peak Firing Pressure for a New Generation of Diesel and Gas Engines

300 bar Peak Firing Pressure for a New Generation of Diesel and Gas Engines

Flame transport in a heavy-duty diesel engine

A heavy-duty diesel engine has been constructed to provide full optical access to the piston bowl with a window forming the bottom of the “optical” piston. The engine is operated up to 1400 rpm, with peak firing pressure of up to 160 bar and IMEP levels of up to 20 bar. Fuel injection is accomplished with a common rail system and an externally driven high-pressure pump. Data were taken for cylinder pressure with synchronous recording of diesel flame ignition and combustion by means of a high-speed camera. The task of the project summarized in this paper was to evaluate flame and cylinder pressure data gained in this engine at part load and high-load operation. The focus of data evaluation was on identifying main flame transport mechanisms and relating them to simultaneously recorded rates of heat release.

Effects on performances, emissions and particle size distributions of a dual fuel (methane-diesel) light-duty engine varying the compression ratio

Economic and technological issues related to meet the future harmful emissions and greenhouse gases (GHG) standards are pushing the scientific community to consider studying alternative routes for low emissions and high efficient propulsion systems. A possible approach is represented by the dual-fuel (DF) concept applied to high efficient compression ignition engines.In this context, the results of a wide experimental campaign performed on a single-cylinder engine platform equipped with modern combustion and injection systems operated in dual-fuel diesel/methane mode are presented. The effects of the compression ratio, injection parameters and air-throttling on the global performances and emissions, also in terms of particle size spectrum, are assessed.The tests were performed in several operating points representative of real working conditions of an automotive light-duty (LD) diesel engine in order to carry out the fuel consumption (FC), the GHG and the pollutant emissions estimation on the New European Driving Cycle (NEDC) test procedure. A proper DF engine parameter calibration was set-up observing constraints in terms of in-cylinder peak firing pressure, pressure rise rate, cycle-to-cycle variation and engine-out emissions.A significant impact of the CR variation and injection parameters on the combustion characteristics and emissions is revealed in DF mode (MHC). In particular, benefits on methane unburnt (MHC) and combustion noise can be attained reducing the CR. A global CO2 reduction of about 12%, over the NEDC, can be definitely obtained with an average CH4 substitution rate of about 50% and independently of the CR at the expense of the DF- CO2 equivalent that is higher (22%) compared to D mode. The DF particles concentration in the accumulation mode is generally reduced as well as the estimated particle number on the NEDC. Moreover, within the tested engine class, a CR of 15.5 appears to be the best compromise among the global efficiency and pollutant emissions outputs to operate in DF mode.