Alternative fuels and combustion modes to lower pollutant emissions from conventional internal combustion engines

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Measurements of Time-Resolved Mass Injection Rates for a Multi-Hole and an Outward Opening Piezo GDI Injector

Time-resolved mass injection rates of an outward opening piezoactuated and a solenoid actuated multi-hole GDI injector were measured to investigate (1) the influence of both hardware and software settings and (2) the influence on the injection rates from a wide range of operational parameters and (3) discuss limitations and issues with this measurement technique. The varied operating parameters were fuel pressure, back-pressure, electrical pulse width,single/double injection and injection frequency. The varied hardware/software parameters were injector protrusion, upstream fuel pressure condition and the cut-off frequency of the software\u27s low-pass filter. Signal quality was found to be dependent on both hardware and software settings, especially the cut-off frequency of the low-passfilter. Measurements with high signal quality were not possible for back-pressures lower than 0.5 MPa. For the smallest possible injections, the piezo-actuated injector was found to be superior since it can inject very small amounts of fuel very accurately with little fuelpressure dependency. For engine realistic back-pressures, the multi-hole injector was found to be back-pressure independent. The piezo injector however was found to be strongly influenced by the back-pressure. The dynamic range was found to be much higher for the piezo injector, and the non-linear flow area was much larger for the multi-hole injector. Both injectors were capable of doubleinjections but the piezo can use shorter dwell times. Effects of upstream fuel pressure fluctuations, especially on the second injection of a double injection, must be carefully taken into account

Method for the recognition of the fuel composition in CNG engines fed with natural gas/biofuel/hydrogen blends

The production of biofuels from biomass gasification results in a wide range of fuel mixture compositions, which have a notable impact on performance and emissions of internal combustion engines. Thus, it is crucial that the composition of the blend being used is automatically identified by the engine control unit, after refueling. Standard ECU hardware is not able to recognize which fuel is actually present in the vehicle tank, hence combustion parameters cannot be changed accordingly. A methodology to perform an estimation of the composition of natural gas/biofuel/hydrogen blends, as it is fueled into CNG engines, is here presented and assessed. Experimental data have been collected in an SI engine, working under different steady-state conditions. Five different fuel blends of known composition have been tested with the same ECU calibration, relative to CNG. The injector has been characterized by means of a linear regression model aiming to predict the injection duration from data readily available in the ECU. A candidate set of 10 different sample blends, representative of the possible wide variety of blends that can be fed to the engine at the fuel pump station, was given as input to the regression model and an error in terms of injection duration has been evaluated. The method has proved to correctly recognize the actual fuel blend within the candidate set, with a maximum error of 5% on hydrogen volume content when HCNG mixtures are considered. The recognition algorithm converges after less than 10 different engine working conditions, in terms of speed and load. The candidate set has been extended to a full factorial set of 2 million blends, to validate the ability of the recognition method to correctly match the real fuel

Analisi sperimentale di una combustione diesel non convenzionale - Ottimizzazione mediante l'applicazione di tecniche statistiche

Una combustione ad elevato grado di premiscelazione è stata implementata in un motore diesel Euro VI, per diminuire contemporaneamente le emissioni di NOx e PM. Tecniche statistiche hanno permesso di ridurre il numero dei test mantenendo un elevato grado di predittvità dell'interazione dei parametri del motore su emissioni, consumi e rumore. Sono state ridotte le emissioni di NOx del 90% e di PM del 99%, a scapito di un aumento del consumo di combustibile e delle emissioni di HC e CO

Influence of Different Compositions of Natural Gas on Engine Performance

The increasing environmental concern, the demographic and economic growth of the emerging economies and the progressive reduction in the world reserves of crude oil forced the transportation sector to consider the use of alternative fuels (natural gas and hydrogen enriched methane) and renewable sources (bio-gases). The processes employed for biogas production are responsible for blends made up by different percentages of methane, CO, H2 and inert gases. Such a variety results into a wide range of heating values as well as chemical and physical properties and inevitably affects the engine combustion process and performance. The present paper investigates the effect of different fuel blends (G20, G25 and HCNG30) on the performance of a 1.4 litre spark ignition engine and specifically it aims at highlighting the need for an algorithm to be implemented in the engine ECU and capable to identify the mixture composition so as to set the proper engine control parameters. Improved combustion behaviour was achieved when hydrogen was added to methane with the drawbacks of reduced engine exhaust temperatures and increased in-cylinder pressure. G25 operations were in turn characterized by a decrease in the engine power output associated with the replacement of methane with inert gases

Influence of Different Compositions of Natural Gas on Engine Performance

The increasing environmental concern, the demographic and economic growth of the emerging economies and the progressive reduction in the world reserves of crude oil forced the transportation sector to consider the use of alternative fuels (natural gas and hydrogen enriched methane) and renewable sources (bio-gases). The processes employed for biogas production are responsible for blends made up by different percentages of methane, CO, H2 and inert gases. Such a variety results into a wide range of heating values as well as chemical and physical properties and inevitably affects the engine combustion process and performance. The present paper investigates the effect of different fuel blends (G20, G25 and HCNG30) on the performance of a 1.4 litre spark ignition engine and specifically it aims at highlighting the need for an algorithm to be implemented in the engine ECU and capable to identify the mixture composition so as to set the proper engine control parameters. Improved combustion behaviour was achieved when hydrogen was added to methane with the drawbacks of reduced engine exhaust temperatures and increased in-cylinder pressure. G25 operations were in turn characterized by a decrease in the engine power output associated with the replacement of methane with inert gases

Zero Dimensional Models for EGR Mass-Rate and EGR Unbalance Estimation in Diesel Engines

A precise estimation of the recirculated exhaust gas rate and oxygen concentration as well as a predictive evaluation of the possible EGR unbalance among cylinders are of paramount importance, especially if non-conventional combustion modes, which require high EGR flow-rates, are implemented. In the present paper, starting from the equation related to convergent nozzles, the EGR mass flow-rate is modeled considering the pressure and the temperature upstream of the EGR control valve, as well as the pressure downstream of it. The restricted flow-area at the valve-seat passage and the discharge coefficient are carefully assessed as functions of the valve lift. Other models were fitted using parameters describing the engine working conditions as inputs, following a semi-physical and a purely statistical approach. The resulting models are then applied to estimate EGR rates to both conventional and non-conventional combustion conditions. In a following step, a correlation was proposed between EGR rate and combustion metrics. This function was then applied to check the possibility of estimating the EGR unbalance, which can negatively affect combustion stability, in particular at high EGR rates. EGR unbalance was also evaluated considering the measurements of the temperature of the charge entering each cylinder. These two methods to evaluate EGR unbalance were then compared to CFD calculations

Steady-State and Transient Operations of a Euro VI 3.0L HD Diesel Engine with Innovative Model-Based and Pressure-Based Combustion Control Techniques

In the present work, different combustion control strategies have been experimentally tested in a heavy-duty 3.0 L Euro VI diesel engine. In particular, closed-loop pressure-based and open-loop model-based techniques, able to perform a real-time control of the center of combustion (MFB50), have been compared with the standard map-based engine calibration in order to highlight their potentialities. In the pressure-based technique, the instantaneous measurement of in-cylinder pressure signal is performed by a pressure transducer, from which the MFB50 can be directly calculated and the start of the injection of the main pulse (SOImain) is set in a closed-loop control to reach the MFB50 target, while the model-based approach exploits a heat release rate predictive model to estimate the MFB50 value and sets the corresponding SOImain in an open-loop control. The experimental campaign involved both steady-state and transient tests. The three control techniques were compared in steady-state tests under various conditions, featuring standard as well as PCCI combustion mode, different kinds of fuels, a disturbance added to the pressure signals from in-cylinder transducers (to simulate the effect of an aged or low-cost pressure transducer) and an injector with a reduced mass flow rate mounted on one cylinder. The behavior of the three controls was tested in transient conditions as well, analyzing in particular fast load and speed ramps. The above mentioned testing conditions were performed to evaluate the robustness of the pressure-based and model-based techniques compared to standard calibration map-based control and their outcomes in terms of engine operation stability. The proposed real-time combustion control techniques provided fuel consumption and emissions in line with the conventional map-based control. In addition, they lead to an improvement in combustion stability, which can be an important issue especially when transient operations are considered or when non-conventional combustion modes, such as PCCI, are implemented

Performance and Emission Comparison between a Conventional Euro VI Diesel Engine and an Optimized PCCI Version and Effect of EGR Cooler Fouling on PCCI Combustion

Premixed charge compression ignition (PCCI) is an advanced combustion mode that has the aim of simultaneously reducing particulate matter and nitrogen oxide exhaust emissions, compared with conventional diesel combustion, thanks to a partially premixed charge and low temperature combustion. In this work, PCCI combustion has been implemented by means of an early single-injection strategy and large amounts of recirculated exhaust gas. Starting from a commercial Euro VI on-road engine, the engine hardware has been modified to optimize PCCI operations. This has involved adopting a smaller turbo group, a new combustion chamber and injectors, and a dedicated high-pressure exhaust gas recirculation system. The results, in terms of engine performance and exhaust emissions, under steady-state operation conditions, are presented in this work, where the original Euro VI calibration of the conventional engine has been compared with the PCCI calibration of the optimized hardware engine. The obtained results show that the engine-out nitrogen oxides and soot were dramatically reduced, and this can offer the possibility of reviewing the after-treatment system. The penalties, in terms of brake specific fuel consumption, were generally below 10%, compared with the Euro VI configuration. The main limitations were derived from the combustion noise and the hydrocarbon and carbon monoxide emissions at the exhaust, which could represent an issue, especially when the exhaust temperature is not high enough to allow the diesel oxidation catalyst to work with high conversion efficiencies. Furthermore, the effect of EGR cooler fouling on the performance and emissions has been presented and discussed. The increased pressure drop across a fouled EGR cooler results in a reduced amount of exhaust gas recirculation, thus posing a serious problem for PCCI calibration activity