Silvana Di Iorio

Assessment of Closed-Loop Combustion Control Capability for Biodiesel Blending Detection and Combustion Impact Mitigation for an Euro5 Automotive Diesel Engine

The present paper describes the results of a cooperative research project between GM Powertrain Europe and Istituto Motori - CNR aimed at studying the impact of both fresh and highly oxidized Rapeseed Methyl Ester (RME) at different levels of blending on performance, emissions and fuel consumption of modern automotive diesel engines featuring Closed-Loop Combustion Control (CLCC). In parallel, the capability of this system to detect the level of biodiesel blending through the use of specific detection algorithms was assessed. The tests were performed on the recently released 2.0L Euro5 GM diesel engine for passenger car application equipped with embedded pressure sensors in the glow plugs. Various blends of fresh and aged RME with reference diesel fuel were tested, notably 20% RME by volume (B20), 50% (B50) and pure RME (B100). The tests on the multi-cylinder engine were carried out in a wide range of engine operating points for the complete characterization of the biodiesel performance in the New European Driving Cycle (NEDC). The results highlighted that there is not appreciable difference in terms of performance and emission between fresh and oxidized biodiesel, at all levels of blending. On the other hand, the capability of the CLCC control to detect biodiesel blending with reasonable accuracy and to implement the corrective actions for avoiding emission drift and performance losses was successfully demonstrated.

Analysis of Particle Mass and Size Emissions from a Catalyzed Diesel Particulate Filter during Regeneration by Means of Actual Injection Strategies in Light Duty Engines

The diesel particulate filters (DPF) are considered the most robust technologies for particle emission reduction both in terms of mass and number. On the other hand, the increase of the backpressure in the exhaust system due to the accumulation of the particles in the filter walls leads to an increase of the engine fuel consumption and engine power reduction. To limit the filter loading, and the backpressure, a periodical regeneration is needed. Because of the growing interest about particle emission both in terms of mass, number and size, it appears important to monitor the evolution of the particle mass and number concentrations and size distribution during the regeneration of the DPFs. For this matter, in the presented work the regeneration of a catalyzed filter was fully analyzed. Particular attention was dedicated to the dynamic evolution both of the thermodynamic parameters and particle emissions. The measurements were performed at the exhaust of a Euro 5 CR Diesel engine equipped with a Close Coupled DPF. The regeneration process was investigated in a point representative of an extraurban engine operating condition. The regeneration was managed by the electronic control unit (ECU). In particular, an injection calibration was implemented taking into account the engine and the filter features. The particle size distribution evolution during regeneration phase was measured in the size range 5-1000 nm using a differential mobility spectrometer. The particle mass concentration was monitored by means of a microsoot sensor. Particle mass and number concentrations strongly increase during the regeneration process. Moreover, a high concentration of the number of particles smaller than 30nm was observed in some critical phases of the regeneration process.

A comprehensive analysis of the impact of biofuels on the performance and emissions from compression and spark-ignition engines:

The compression ignition and small displacement spark-ignition engines play an important role in the urban air pollution. In particular, vehicles equipped with compression ignition engines are widely used because of their higher performance and fuel efficiency with respect to the spark-ignition ones. Nevertheless, spark-ignition engines with low displacements are even more wide-spreading because of the lower fuel consumption and emissions. They are also used for two-wheeled vehicles, whose easier navigation makes them widely used in heavily congested areas. Their contribution on urban pollution is worsened by the fact that these vehicles have to comply with the Euro 3 standard; light vehicles have, instead, to fulfill the more restrictive Euro 6, which for the compression ignition and gasoline direct injection engines indicates for particle emissions also a number-based regulation. This article aims to characterize the effects of biofuels on engine emissions and performance of compression ignition and spark-ignition engines. The investigation was carried out on different class of engines. Direct injection and a port fuel injection spark-ignition engines fueled with ethanol and its blends, 10 v/v%, 50 v/v% and 85 v/v% of ethanol in gasoline. The compression ignition engine was equipped with a common rail injection system and was fueled with pure rapeseed methyl ester, representative of fatty acid methyl ester, and its blends in diesel, 20 v/v% and 50 v/v%. The gaseous emissions and the particle concentration were measured at the exhaust by means of conventional instruments. Particle size distribution function was measured in the range from 5.6 to 560 nm by means of an engine exhaust particle sizer. A comprehensive characterization of the particulate carbon was performed by means of optical diagnostics in the combustion chamber. In particular, two-dimensional images of flame evolution were detected and processed by two-color pyrometry technique to assess the in-cylinder soot formation and oxidation processes. For both the investigated spark-ignition and compression ignition engines, the use of biofuels shows a partial increase in the specific fuel consumption and a reduction of the soot particles emission. Nevertheless, a further effort on engine technology should be paid to balance the mass with the size and number of the particles.

Characterization of Soot Particles Produced in a Transparent Research CR DI Diesel Engine Operating with Conventional and Advanced Combustion Strategies

The effect of the combustion mode on particle emission was analyzed both in the cylinder and at the exhaust of a direct injection (DI) Common Rail (CR) transparent research diesel engine by means of spectroscopic and conventional methods. The engine was equipped with a flexible electronic control unit (ECU) capable of operating up to 5 injections per cycle with different start of injection and dwell time allowing performing different combustion modes. The conventional diesel combustion, the homogeneous charge compression ignition (HCCI), and the low temperature combustion (LTC) modes were analyzed. In-cylinder broadband UV–visible scattering and extinction measurements were carried out to follow the particle formation and oxidation processes as well as to have information about their chemical nature and size distribution. The characterization of the particulate emission at the exhaust was performed by means of an electrical low pressure impactor (ELPI), for the counting and the sizing of the particles, and an opacimeter, for measuring the smoke opacity. The in-cylinder measurements highlighted that particles ranged from 3 to 100 nm whatever was the combustion mode. Nevertheless, particles produced by a conventional diesel combustion process principally consist of soot. Whereas particles formed during HCCI and LTC modes are composed mainly of organic compounds. The exhaust particle emissions depend on the combustion mode both in terms of size and number. A larger amount of particles smaller than 100 nm was emitted during HCCI and LTC modes with respect to the conventional one. Moreover, HCCI mode showed a strong accumulation mode. Copyright 2012 American Association for Aerosol Research

The Key Role of the Electronic Control Technology in the Exploitation of the Alternative Renewable Fuels for Future Green, Efficient and Clean Diesel Engines

Great concerns are growing up on environmental impact of fossil fuel and poor air quality in urban areas due to traffic-related air pollution. In the last years, special attention was paid mainly to particulate matter (PM) and NOx emissions of diesel engines since these pollutants are associated to environmental and health issues. In particular, NOx contributes to the formation of ozone and acid rains and PM could cause injuries to the pulmonary and the cardiovascular systems. Nowadays, the overall concern about the global warming determines an increased interest also for CO2 emissions, one of the major greenhouse gas (GHG). In this respect, a significant improvement can be reached with the increased use of ‘‘clean’’ and renewable fuels. It is well known, in fact, that the use of biofuels can contribute to a significant well-to-wheel (WTW) reduction of GHG emissions. The most interesting biofuel is the biodiesel and the fuels synthesised from fossil or biogenic gas. Biodiesel designates a wide range of methyl-esters blends and is generally indicated with the acronym FAME, Fatty-Acid Methyl Esters. Biodiesel is produced from vegetable oils and animal fats through the transesterification, an energy efficient process that gives a significant advantage in terms of CO2 emission and that features both high energy conversion efficiency and fuel yield from processed oil. These two characteristics are the main responsible for the overall GHG emissions benefit of biodiesel in WTW analyses [1]. More recently, starting from the well-known Fischer-Tropsch synthesis process, another generation of alternative diesel fuel was developed. It is usually indicated with XTL, where X denotes the specific source feedstock and TL (to Liquid) highlights the final liquid state of the fuel. It has minor interferences with the human food chain, since non-edible biomasses can be employed or, in case of animal-edible biomasses, the whole plant can be processed, as for the cellulosic ethanol production. From the engine fuelling point of view, the significant difference between the two biofuels lies in their chemical composition. The first is essentially a blend of methyl-esters and the second of paraffin and olefin hydrocarbons. Because of the growing concerns about the energy crops impact on environment and food price, an increasing number of countries and stakeholders have recently challenged FAME biofuels. On the contrary, the XTL fuels, which

Optimization of the compressed natural gas direct injection in a small research spark ignition engine

The permanent aim of the automotive industry is the further improvement of the engine efficiency and the simultaneous pollutant emissions reduction. In order to optimize the small internal combustion engines, it is necessary to further improve the basic knowledge of the thermo-fluid dynamic phenomena occurring during the combustion process. In this context, the application of optical diagnostic techniques permits a deep insight into the fundamental processes such as flow development, fuel injection, and combustion process. The aim of this study was the optimization of the compressed natural gas direct injection by means of the analysis of the injection phase and combustion process. This analysis allowed the improvement of the engine efficiency in lean-burn operation condition too. The investigation was carried out in an optically accessible small direct injection spark ignition single-cylinder engine. Two different injectors were tested. The first one was the injector designed according to the results of model simulation, and the second one was a modified prototype obtained using the findings of the optical analysis carried out in the combustion chamber. The characteristic parameters of the gaseous fuel jet were evaluated through an image processing procedure. The fuel rail was modified in order to allow the injection of seeding particles into the gaseous fuel. The gas jet was analyzed using a white light source coupled with a high spatial and temporal resolution fast camera. The combustion process development was investigated for same engine operative condition performing a cycle-resolved visualization of the flame. Moreover, this methodology permitted the evaluation of motion field and turbulence during the injection process directly into the combustion chamber. The results of investigation evidenced that the modification of the injector, designed according to the optical analysis made in the optically accessible engine, allowed an optimization of compressed natural gas direct injection resulting in improved combustion and emissions reduction.

Optical Characterization of Methane Combustion in a Four Stroke Engine for Two Wheel Application

In the urban area the internal combustion engines are the main source of CO2, NOx and particulate matter (PM) emissions. The reduction of these emissions is no more an option, but a necessity highlighted by the even stricter emission standards. In the last years, even more attention was paid to the alternative fuels. They allows both reducing the fuel consumption and the pollutant emissions. Regarding the gaseous fuels, methane is considered one of the most interesting in terms of engine application. It represents an immediate advantage over other hydrocarbon fuels because of the lower C/H ratio. In this paper the effect of the methane on the combustion process, the pollutant emissions and the engine performance was analyzed. The measurements were carried out in an optically accessible singlecylinder, Port Fuel Injection, four-stroke SI engine equipped with the cylinder head of a commercial 250 cc motorcycles engine and fuelled both with gasoline and methane. Optical measurements were performed to analyze the combustion process with a high spatial and temporal resolution. In particular, optical techniques based on 2D-digital imaging were used to follow the flame propagation in the combustion chamber. UV-visible spectroscopy allows detecting the chemical markers of combustion process such as the radicals OH and CH. The exhaust emissions were characterized by means of a gaseous analyzer and an opacimeter. The measurements were performed under steady state conditions, at 2000rpm at minimum and full load. Introduction In the urban area the internal combustion engines are the main source of CO2, NOx and particulate matter (PM) emissions. The reduction of these emissions is no more an option, but a necessity highlighted by the even stricter emission standards. In the last years, even more attention was paid to the alternative fuels that allow both reducing the fuel consumption and the pollutant emissions. Methane is a promising alternative fuel to petrol for internal combustion engines [1]. It represents an immediate advantage over other hydrocarbon fuels because of the lower C/H ratio. Moreover, it has a higher Lower Heating Value (LHV) and stoichiometric air/fuel ratio and a higher Research Octane Number (RON) which permits higher compression ratios, higher boost in turbocharged engines, and better knocks limited XXXIV Meeting of the Italian Section of the Combustion Institute 2 spark advances, as reduces the knock sensitivity. The major drawback of the use of methane in the spark ignition or compression ignition engines is the low flame propagation speed. The flame front propagation speed depends mainly on the turbulence and the air/fuel ratio. In particular, it increases at the increasing of the turbulence and at the decreasing of the air/fuel ratio [2]. In this paper the effect of the methane on the combustion process, the pollutant emissions and the engine performance was analyzed. The measurements were carried out in an optically accessible single-cylinder, Port Fuel Injection, fourstroke SI engine equipped with the cylinder head of a commercial 250 cc motorcycles engine. Optical measurements were performed to analyze the combustion process with a high spatial and temporal resolution. In particular, optical techniques based on 2D-digital imaging were used to follow the flame propagation in the combustion chamber. UV-visible spectroscopy allows detecting the chemical markers of combustion process such as the radicals OH and CH. The measurements were performed under steady state conditions, at 2000 rpm at minimum and full load. The engine was fuelled with commercial gasoline and methane. Experimental Apparatus Transparent Engine The experimental activity was performed in an optically accessible single-cylinder, Port Fuel Injection, four-stroke SI engine [3]. The engine bore and stroke were 72 mm and 60 mm, respectively. The geometric compression ratio was 11:1. The engine was equipped with the cylinder head of a commercial 250 cc motorcycles engine. A four-valve, pent-roof chamber engine was mounted on an elongated piston. The engine reached a maximum speed of 5000 rpm. The maximum performance is: 7.9 kW and 14.7 Nm at 5000 rpm. The head had a centrally located spark plug and a quartz pressure transducer was flush-installed in the combustion chamber to measure the combustion pressure. The in-cylinder pressure, the rate of chemical energy release and the related parameters were evaluated on an individual cycle basis and/or averaged on 400 cycles [2]. The optical engine was characterized by an elongated cylinder and a piston provided with a sapphire window which replaces the flat-bottom piston bowl. The engine is also equipped with a quartz cylinder in order to have a lateral point of view of the combustion chamber. This system enables the passage of optical signals coming from the combustion chamber. To reduce the window contamination by lubricating oil, the elongated piston arrangement was used together with self-lubricating Teflonbronze composite piston rings in the optical section. Setup for Spectroscopic Measurements During the combustion process, the light passed through the sapphire window and it was reflected toward the optical detection assembly by a 45° inclined UV-visible XXXIV Meeting of the Italian Section of the Combustion Institute 3 mirror located in bottom of the engine. Chemiluminescence signals were collected and focused on the entrance slit of a spectrograph through an UV-Visible objective. The slit was 250 μm wide open and it was located in front of the combustion chamber. Spectrograph was 15 cm focal length, f/4 luminous, and equipped with a grating of 300 g/mm, blazed at 300 nm, with a dispersion of 3.1 nm/mm. The spectral image formed on the spectrograph exit plane was matched with a gated intensified CCD camera. Data were detected with the spectrograph placed at two central wavelengths, 375 and 625 nm, respectively, and the intensifier-gate duration was set to 166.6 μs in order to have a good accuracy in the timing of the different investigated events. Chemiluminescence signals, due to radical emission species, were detected in the central and lateral locations of the combustion chamber with high spatial and temporal resolution. Engine synchronization with ICCD camera was obtained by the unit delay connected to the signal coming from the engine shaft encoder. In this way, it was possible to determine the crank angles where optical data were detected. Engine Operating Conditions All the experimental investigations were carried out at 2000 rpm. The intake air temperature was fixed at 298 K and the cooling water temperature was set at 333 K. Commercial gasoline and methane fuels were used. For all the test cases, the injection-duration (DOI) was chosen to obtain a stoichiometric equivalence ratio. Two different fuel injection strategies were tested for both fuels: minimum load (closed throttle) and full load (wide open throttle). The coefficient of lambda value variation was measured on 400 consecutive cycles. It was lower than 1.8% for all the selected conditions. The spark timing (SOS) was always fixed to operate at the maximum brake torque. More details about the operating conditions are reported in Table 1. Table 1. Engine operating conditions Test label Fuel Pinj [bar] DOI [cad] SOS [cad] Minimum load Gasoline 3.5 29.5 -29.5 Full load Gasoline 3.5 71 -71 Minimum load Methane 1.5 128.7 -378.7 Full load Methane 1.5 250.6 -500.6 Results and Discussion The measurements were performed from the Start of Spark (SOS) until exhaust valve opening. The spectroscopic measurements were binned along space direction in order to obtain three typical locations: in correspondence of the exhaust valves, the spark plug and the intake valves. The development of the combustion process was identified by means of the analysis of digital images. In particular, the flame front propagation speed, an XXXIV Meeting of the Italian Section of the Combustion Institute 4 important parameter in the study of combustion in spark-ignition engines, was evaluated. The comparison between the flame front propagation speed, for the gasoline and methane fuels at minimum and full load is reported in Figure 1. -20 -10 0 10 crank angle [degree] 0 4 8 12 16 fla m e fro nt p ro pa ga tio n sp ee d [m /s ] minimum load Gasoline

Soot particle size and pollutant emissions characterisation from an LD diesel engine equipped with high-pressure and low-pressure EGR system and operating with conventional and PCCI combustion

The paper analyses the soot Particle Size Distribution Function (PSDF) measurements carried out at the exhaust of a modern automotive diesel engine equipped with a low-pressure Exhaust Gas Recirculation (EGR) system and operating with conventional and Premixed Charge Compression Ignition (PCCI). The results have indicated significant benefits in terms of exhaust raw particle number emission with the adoption of low-pressure EGR system and PCCI calibration and, thanks to the peculiarity of the operating mode of Low Pressure EGR (LPEGR) system, have highlighted the complex link between in-cylinder charge composition and the PSDF characteristics.