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In this work, the authors evaluate the energetic and economic advantages connected to the implementation of an electric Kinetic Energy Recovery System (e-KERS) on an internal combustion engine vehicle (ICEV). The e-KERS proposed is based on the use of a supercapacitor (SC) as energy storage element, a brushless motor generator unit (MGU) for the conversion of the vehicle kinetic energy into electric energy (and vice versa), and a power converter properly designed to manage the power transfer between SC and MGU. The low complexity of the system proposed, the moderate volume and weight of the components selected for its assembly, together with their immediate availability on the market, make the solution presented ready for the introduction in current vehicle production. A widely diffused passenger car, endowed of a gasoline fuelled spark ignition engines, was selected for the evaluation of the advantage connected to the implementation of the e-KERS.

Internal combustion engine modeling is nowadays a widely employed tool for modern engine development. Zero and mono dimensional models of the intake and exhaust systems, combined with multi-zone combustion models, proved to be reliable enough for the accurate evaluation of in-cylinder pressure, which in turn allow the estimation of the engine performance in terms of indicated mean effective pressure (IMEP). In order to evaluate the net engine output, both the torque dissipation due to friction and the energy drawn by accessories must be taken into consideration, hence a model for the friction mean effective pressure (FMEP) evaluation is needed.

Hybrid powertrains utilize an engine to benefit from the power density of the liquid fuel to extend the range of the vehicle. On the other hand, the electric machine is used for; transient operation, for very low loads and where legislation prohibits any gaseous and particulate emissions. Consequently, the operating points of an engine nowadays shifted from its conventional, broad range of speed and load to a narrower operating range of high thermal efficiency. This requires a departure from conventional engine architecture, meaning that analytical models used to predict the behavior of the engines early in the design cycle are no longer always applicable. Friction models are an example of sub-models which struggle with previously unexplored engine architectures. The “pressurized motored” method has proven to be a simple experimental setup which allows a robust FMEP determination against which engine friction simulation can be fine-tuned.

The performance of a spark ignition engine strongly depends on the phase of the combustion process with respect to piston motion, and hence on the spark advance; this fundamental parameter is actually controlled in open-loop by means of maps drawn up on the test bench and stored in the Electronic Control Unit (ECU). Bi-fuel engines (e.g. running either on gasoline or on natural gas) require a double mapping process in order to obtain a spark timing map for each of the fuels. This map based open-loop control however does not assure to run the engine always with the best spark timing, which can be influenced by many factors, like ambient condition of pressure, temperature and humidity, fuel properties, engine wear. A feedback control instead can maintain the spark advance at its optimal value apart from operative and boundary conditions, so as to gain the best performance (or minimum fuel consumption).

The variation of in-cylinder heat transfer with parameters such as engine speed, air-to-fuel ratio, coolant temperature and compression ratio were frequently studied in classical research. These experimentally-obtained relationships are important for improving in-cylinder heat transfer models, essential in developing CO2 reducing strategies. In this publication, a 2.0 liter compression ignition engine was tested in the pressurized motored configuration. This developed experimental setup allowed testing of the engine at speeds ranging between 1400 rpm and 3000 rpm, with peak in-cylinder gas pressures from 40 bar to 100 bar. The engine was motored using different gas compositions chosen specifically to have ratios of specific heats of 1.40, 1.50, 1.60 and 1.67 at room temperature. This enabled motored testing with peak in-cylinder bulk gas temperatures ranging from 700 K to 1500 K.

In the ever increasing challenge of developing more efficient and less polluting engines, friction reduction is of significant importance and its investigation needs an accurate and reliable measurement technique. The Pressurized Motoring method is one of the techniques used for both friction and heat transfer measurements in internal combustion engines. This method is able to simulate mechanical loading on the engine components similar to the fired conditions. It also allows measurement of friction mean effective pressure (FMEP) with a much smaller uncertainty as opposed to that achieved from a typical firing setup. Despite its advantages, the FMEP measurements obtained by this method are usually criticized over the fact that the thermal conditions imposed in pressurized motoring are far detached from those seen in fired conditions. In light of these considerations, the authors have put forward a modification to the method, employing Argon in place of Air as pressurization medium.

Mechanical friction is a significant power dissipater in the internal combustion engine. In the effort of designing more efficient and less pollutant engines, friction reduction is certainly on the agenda to be investigated. Such investigation cannot be possible without an accurate measurement of the same quantity. This publication regards a continued study on the mechanical friction determination in an internal combustion engine using the Pressurised Motoring Method. In this work, the friction mean effective pressure of a four-cylinder compression ignition engine was investigated with varying engine speed and manifold pressurisation, using a dedicated high precision sensor for the correct determination of the cylinder Top Dead Centre position.

Mechanical friction and heat transfer in internal combustion engines have long been studied through both experimental and numerical simulation. This publication presents a continuation study on a Pressurized Motoring setup, which was presented in SAE paper 2018-01-0121 and found to offer robust measurements at relatively low investment and running cost. Apart from the limitation that the peak in-cylinder pressure occurs around 1 DegCA BTDC, the pressurized motoring method is often criticized on the fact that the gas temperatures in motoring are much lower than that in fired engines, hence might reflect in a different FMEP measurement. In the work presented in SAE paper 2019-01-0930, Argon was used as the pressurization gas due to its high ratio of specific heats. This allowed to achieve higher peak in-cylinder temperatures which close further the gap between fired and motored mechanical friction tests.

Heat transfer from the cylinder of internal combustion engines has been studied for decades, both in motored and fired configurations. Its understanding remains fundamental to the optimization of engine structures and sub-systems due to its direct effect on reliability, thermal efficiency and gaseous emissions. Experimental measurements are usually conducted using fast response surface thermometers, which give the instantaneous cylinder surface temperature. The transient component of heat flux through the cylinder wall was traditionally obtained from a spectral analysis of the surface temperature fluctuation, whereas the steady-state component was obtained from Fourier’s law of conduction. This computation inherently assumes that heat flows in one-dimension, perpendicular to the heated surface in a semi-infinite solid with constant thermo-physical properties.

Bi-fuel spark ignition engines, nowadays widely spread, are usually equipped with two independent injection systems, in order run the engine either with gasoline or with gaseous fuel, which can be Natural Gas (NG) or Liquefied Petroleum Gas (LPG). These gases, besides lower cost and environmental impact, are also characterized by a higher knock resistance with respect to gasoline that allows to adopt a stoichiometric proportion with air also at full load. Gasoline, on the other hand, being injected as liquid, maintains higher volumetric efficiency and hence higher power output.

In the last years new and stricter pollutant emission regulations together with raised cost of conventional fuels resulted in an increased use of gaseous fuels, such as Natural Gas (NG) or Liquefied Petroleum Gas (LPG), for passenger vehicles. Bi-fuel engines represent a transition phase product, allowing to run either with gasoline or with gas, and for this reason are equipped with two separate injection systems. When operating at high loads with gasoline, however, these engines require rich mixtures and retarded combustions in order to prevent from dangerous knocking phenomena: this causes high hydrocarbon (HC) and carbon monoxide (CO) emissions together with high fuel consumption.

Natural gas represents today maybe the most valid alternative to conventional fuels for road vehicles propulsion. The main constituent of natural gas, methane, is characterized by a high autoignition temperature, which makes the fuel highly resistant to knocking: this allows a considerable downsizing of the engine by means of supercharging even under high compression ratio. Starting from these considerations, the authors realized a thermodynamic model of a 4-cilynder s.i. engine for the prevision of in-cylinder pressure, employing a two-zone approach for the combustion and adding sub-models to account for gas properties change and knocking occurrence. An extensive experimental campaign has been carried out on the test bed, equipped with a naturally aspirated bi-fuel s.i. engine (i.e. an engine which can run either with gasoline or with compressed natural gas), so as to set the model constants to the best matching values.

As is known gaseous fuels, such as Liquefied Petroleum Gas (LPG) and Natural Gas (NG), thanks to their good mixing capabilities, allow complete and cleaner combustion than normal gasoline, resulting in lower pollutant emissions and particulate matter. Some of the automobile producers already put on the market “bi-fuel” engines, which may be fed either with standard gasoline or with LPG. These engines, endowed of two separate injection systems, are originally designed for gasoline operation; hence they do not fully exploit the good qualities of LPG, such as its better knocking resistance, which would allow higher compression ratios. Moreover, when running with gasoline at medium high loads, the engine is often operated with rich mixture and low spark advance (with respect to the maximum brake torque value) in order to prevent from dangerous knocking phenomena: this produces both high hydrocarbon and carbon monoxide emissions and high fuel consumption.

The efficiency of Hybrid Electric Vehicles (HEVs) may be substantially increased if the unexpanded exhaust gas energy is efficiently recovered and employed for vehicle propulsion. This can be accomplished employing a properly designed exhaust gas turbine connected to a suitable generator whose output electric energy is stored in the vehicle storage system; a new hybrid propulsion system is hence delineated, where the power delivered by the main engine is combined to the power produced by the exhaust gas turbo-generator: previous studies, carried out under some simplifying assumptions, showed potential vehicle efficiency increments up to 15% with respect to a traditional turbocharged engine. Given the power target of the required exhaust gas turbo-generator, no commercial or reference product could be considered: on account of this, in the preliminary evaluations, the turbine efficiency was assumed constant.

It is known to internal combustion researcher that the correct determination of the crank position when the piston is at Top Dead Centre (TDC) is very important, since an error of 1 crank angle degree (CAD) can cause up to a 10% evaluation error on indicated mean effective pressure (IMEP) and a 25% error on the heat released by the combustion: the TDC position should be then known within a precision of 0.1 CAD. This task can be accomplished by means of a dedicated capacitive sensor, which allows a measurement within the required 0.1 degrees precision. Such a sensor has a substantial cost and its use is not really fast; a different approach can be followed using a thermodynamic method, whose input is the pressure curve sampled during the compression and expansion strokes of a “motored” (i.e. without combustion) cylinder. In this work the authors compare an original thermodynamic method with other ones available in literature, by means of both experimental and simulated pressure curves.

Mechanical friction and heat transfer in internal combustion engines are two highly researched topics, due to their importance on the mechanical and thermal efficiencies of the engine. Despite the research efforts that were done throughout the years on both these subjects, engine modeling is still somewhat limited by the use of sub-models which do not fully represent the phenomena happening in the engine. Developing new models require experimental data which is accurate, repeatable and which covers wide range of operation. In SAE 2018-01-0121, the conventional pressurized motored method was investigated and compared with other friction determination methods. The pressurized motored method proved to offer a good intermediate between the conventional motored tests, which offer good repeatability, and the fired tests which provide the real operating conditions, but lacks repeatability and accuracy.

As is known, internal combustion engines based on Otto or Diesel cycles cannot complete the expansion process of the gas inside the cylinder, thus losing a relevant energy content, in the order of 30% of total. The residual energy of the unexpanded gas has been partially exploited through the use of an exhaust gas turbine for turbocharging the internal combustion engine; further attempts have been made with several compound solutions, with an electric generator connected to the turbocharger allowing to convert into electrical energy the quota power produced by the turbine which is not used by the compressor, or with a second turbine downstream the first to increase the exhaust gas energy recovery. Turbo-compound solutions were also employed in large marine Diesel engines, where the second turbine downstream the first was used to deliver more power to the main propeller shaft. In all these cases the overall efficiency increments remained within 5%.

In-cylinder pressure analysis is becoming more and more important both for research and development purpose and for control and diagnosis of internal combustion engines; directly measured by means of a combustion chamber pressure transducers or evaluated by analysing instantaneous engine speed [1,2,3,4], in-cylinder pressure allows the evaluation of indicated mean effective pressure (IMEP), combustion heat release, combustion phase, friction pressure, etc…It is well known to internal combustion engine researchers that for a right evaluation of these quantities the exact determination of Top Dead Centre (TDC) is of vital importance: a 1° error on TDC determination can lead to evaluation errors of about 10% on the IMEP and 25% on the heat released by the combustion.