This paper presents an original methodology for the instantaneous in-cylinder pressure waveform reconstruction in a spark-ignited internal combustion engine. The methodology is based on the existence of a linear correlation, characterized by frequency response functions, between in-cylinder pressure and engine speed signals. This correlation is experimentally verified and evaluated by simultaneous measurements of the above-mentioned quantities. The evaluation of different frequency response functions, one for each steady-state condition investigated, allows recovering the pressure waveform even under other engine running conditions (i.e., transients). In this way, during on-board operation, the pressure waveform could be recovered using only the engine speed signal, already present in current production electronic control units. In this paper the signal processing methodology and some experimental results, obtained during transient tests, are presented. The methodology could be interesting for the development of advanced engine control strategies aimed at the management of the torque generated by the engine. As an example, traction control in drive-by-wire systems could be a possible challenging application. The in-cylinder pressure reconstruction performed using the frequency response functions, in fact, allows the evaluation of the indicated torque. An important characteristic of this methodology is, furthermore, the diagnostic capability for the combustion process, that is guaranteed by the linear correlation between in-cylinder pressure and instantaneous engine speed waveforms. Also in presence of a misfiring cylinder, when the instantaneous engine speed waveform is strongly affected by the absence of combustion, the reconstructed in-cylinder pressure shows a good agreement with the measured one. The experimental tests have been conducted in a test cell using a four-cylinder production engine. It has to be noted, anyway, that the same methodology can be applied to engines with a higher number of cylinders.

Gasoline engines can be affected, under certain operating conditions, by knocking combustions, which can result in serious engine damage. Specific power and efficiency are influenced by factors such as compression ratio and spark advance regulation, that modify the combustion development over the crank angle: the trade-off between performance and the risk of irreversible damages is still a key factor in the design of both high-performance (racing) and low-consumption engines. New generation detection systems, especially based on ionization current technology, allow aggressive advance mapping and control, and future equipment, such as low-cost in-cylinder pressure transducers, will allow following that trend. Also HCCI (Homogeneous Charge Compression Ignition) engines need a sophisticated combustion monitoring methodology, since increasing BMEP levels in HCCI mode force the combustion to approach the knocking operation. Many methodologies can be found in the literature to recognize potentially dangerous combustions, usually based on the analysis of accelerometer, in-cylinder pressure or ionization current signals. Signals are sampled with high sample rates, then filtered, for a clear recognition of the phenomenon. Filtered signals can then be used to define damage-related indexes, by means of various types of mathematical operations. The indexes are then compared to pre-defined thresholds, for the diagnosis of dangerous combustion events. Thresholds setting is a challenging task, since indexes are not usually intrinsically related to the damages caused by abnormal combustion events. Furthermore, the indexes values usually strongly depend on the engine operating conditions (speed and load), and thresholds must therefore vary with respect to speed and load. It can be said that indexes generally depend on the combustion development over the crank angle, and not necessarily on the knock phenomenon. This means that the index value is also influenced by the spark advance regulation, even without knock. This paper shows why commonly used indexes values vary with engine running conditions, and how raw indexes can be modified in order to obtain an operating conditions independent information. In-cylinder pressure data are analyzed both in the time and frequency domains, in order to show how parameters such as window angular position and width, and band-pass filter characteristics influence the filtered in-cylinder pressure signals, and, as a consequence, knock indexes. Such parameters can affect both the signal to noise ratio and the operating condition dependence, thus they must be carefully optimized. Once operating conditions effects on knock indexes are known, they can be taken into account for indexes evaluation, letting emerge the plain knock effect. This compensation can be carried out in many ways: in the paper two possible methodologies are considered and compared. Both of them perform an index normalization, the first one in the time domain, the second one in the frequency domain. The frequency-domain normalization methodology proves to be efficient in finding operating conditions-independent knock indexes, allowing an a significant reduction of the calibration time. The time-domain methodology is more influenced by the window choice

One of the most effective factors influencing performance, efficiency, and pollutant emissions of internal combustion engines is the combustion phasing: in gasoline engines electronic control units (ECUs) manage the spark advance (SA) in order to set the optimal combustion phase. Combustion control is assuming a crucial role in reducing engine tailpipe emissions and maximizing performance. The number of actuations influencing the combustion is increasing, and as a consequence, the calibration of control parameters is becoming challenging. One of the most effective factors influencing performance and efficiency is the combustion phasing: for gasoline engines, control variables such as SA, air-to-fuel ratio (AFR), variable valve timing (VVT), and exhaust gas recirculation (EGR) are mostly used to set the combustion phasing. The optimal control setting can be chosen according to a target function (cost or merit function), taking into account performance indicators, such as indicated mean effective pressure (IMEP), brake-specific fuel consumption (BSFC), pollutant emissions, or other indexes inherent to reliability issues, such as exhaust gas temperature or knock intensity. Many different approaches can be used to reach the best calibration settings: design of experiment (DOE) is a common option when many parameters influence the results, but other methodologies are in use: some of them are based on the knowledge of the controlled system behavior by means of models that are identified during the calibration process. The paper proposes the use of a different concept, based on the extremum seeking approach. The main idea consists in changing the values of each control parameter at the same time, identifying its effect on the monitored target function, and allowing to shift automatically the control setting towards the optimum solution throughout the calibration procedure. An original technique for the recognition of control parameters variations effect on the target function is introduced, based on spectral analysis. The methodology has been applied to data referring to different engines and operating conditions, using IMEP, exhaust temperature, and knock intensity for the definition of the target function and using SA and AFR as control variables. The approach proved to be efficient in reaching the optimum control setting, showing that the optimal setting can be achieved rapidly and consistently.

While the Diesel Particulate Filter (DPF) is actually a quasi-standard equipment in the European Diesel passenger cars market, an interesting solution to fulfill NOx emission limits for the next EU 6 legislation is the application of a Selective Catalytic Reduction (SCR) system on the exhaust line, to drastically reduce NOx emissions.In this context, one of the main issues is the performance of the SCR system during cold start and warm up phases of the engine. The exhaust temperature is too low to allow thermal activation of the reactor and, consequently, to promote high conversion efficiency and significant NOx concentration reduction. This is increasingly evident the smaller the engine displacement, because of its lower exhaust system temperature (reduced gross power while producing the same net power, i.e., higher efficiency).The proposal of the underlying work is to investigate and identify optimal exhaust line heating strategies, to provide a fast activation of the catalytic reactions on SCR. The main constrain is to limit the potential fuel consumption increase, and possibly to even increase global efficiency, and the chosen application is a small EU5-compliant diesel engine.After an initial investigation, the research has been focused on main combustion control parameters, rather than on post-oxidation processes associated with late injections, in an effort to reduce eventual fuel penalties. The effect of each relevant engine control parameter has been analyzed on the test bench, observing the results in terms of exhaust system temperature and fuel efficiency. After this preliminary identification phase, different calibration strategies have been tested on the vehicle, executing several NEDC cycles. The most relevant comparisons are illustrated and critically discussed in the paper.

In modern Diesel engine control strategies the guideline is to perform an efficient combustion control, mainly due to the increasing request to reduce pollutant emissions. Innovative control algorithms for optimal combustion positioning require the on-board evaluation of a large number of quantities. In order to perform closed-loop combustion control, one of the most important parameters to estimate on-board is MFB50, i.e. the angular position in which 50% of fuel mass burned within an engine cycle is reached. Furthermore, MFB50 allows determining the kind of combustion that takes place in the combustion chamber, therefore knowing such quantity is crucial for newly developed low temperature combustion applications (such as HCCI, HCLI, distinguished by very low NOx emissions). The aim of this work is to develop a virtual combustion sensor, that provides MFB50 estimated value as a function of quantities that can be monitored real-time by the Electronic Control Unit (ECU).Modern technologies for Common Rail Multi-Jet Diesel engines allow designing injection patterns with many degrees of freedom, due to the large number of tunable injection parameters (such as rail pressure, start and duration of each injection….). First, this paper describes a model of the combustion process developed in order to evaluate the energy release within the cylinder. A zero-dimensional approach based on the Wiebe function has been chosen, because it allows obtaining a model which is accurate enough for the analysis at a low computational cost. Once the combustion model has been developed it can be used to determine MFB50. The second section of this paper describes the existing correlations between the injection parameters and the identified Wiebe parameters. These correlations can be used for heat release and MFB50 on board estimation.Experimental tests have been performed running a turbocharged Common Rail Multi-Jet Diesel engine (with up to 4 injections within the same engine cycle) in order to determine the accuracy of the methodology.The described approach allows evaluating MFB50 as a function of the injection parameters as well as other quantities that can be monitored real-time by the ECU. Additional sensors are not necessary for this methodology, therefore it requires no extra cost.

Combustion control is one of the key factors to obtain better performance and lower pollutants emissions, for diesel, spark ignition and HCCI engines. This paper describes a real-time indicating system based on commercially available hardware and software, which allows the real-time evaluation of Indicated Mean Effective Pressure (IMEP) and Rate of Heat Release (ROHR) related parameters, such as 50%MFB, cylinder by cylinder, cycle by cycle. This kind of information is crucial for engine mapping and can be very important also for rapid control prototyping purposes. The project objective is to create a system able to process in-cylinder pressure signals in the angular domain without the need for crankshaft encoder, for example using as angular reference the signal coming from a standard equipment sensor wheel. This feature can be useful both for test bench and on-board tests. In order to gain reliable results or acceptable precision on ROHR-related parameters (ROHR peak & 50%MFB, for example) a high sampling rate is required for the in-cylinder pressure. Since the angular reference signal can have low angular resolution (6 degrees with a typical sensor wheel), the in-cylinder pressure signal sampling rate must be higher than the crankshaft signal frequency. The choice for this application has been to use a high sample rate on a time base for the cylinder pressure signal, performing the transformation from the time domain to the angular domain (necessary in order to evaluate the indicating parameters) by means of an interpolation algorithm. The system features a signal conditioning module allowing to plug directly VRS/Hall effect/encoder as reference sensors; the signals, thus converted to TTL level, are digitally sampled at high frequency for the crankshaft position recognition. In-cylinder pressure signals, instead, are sampled @ 100kHz. The conversion of these samples from the time domain to the angular domain is triggered by the sensor wheel signal. The algorithm used for the conversion can be time and memory consuming: the paper shows that the methodology used is crucial in order to save hardware resources, i.e. to increase the number of analyzed signals. As regards the hardware choice, many requirements have been taken into account: portability, sampling rate, computational power, programming language, external devices interface etc. The final solution is based on a portable Real-Time/FPGA based hardware, which allows performing all the necessary I/O functions and calculations in real time, even at high engine speed and with a high number of cylinders.