In-cylinder Pressure Measurements Research Articles

Effects of high ignition energy on lean combustion characteristics of natural gas using an optical engine with a high compression ratio

Natural gas engines often suffer from slow-burning rate and large cyclic variations, which significantly affects engine performance and thermal efficiency. In this study, using an optical spark-ignition engine with a high compression ratio, the role of high ignition energy in lean combustion characteristics of natural gas was investigated. Synchronization measurement of in-cylinder pressure and visualization images were performed to analyze the correlations of engine performance and combustion characteristics. The results show that elevating ignition energy can improve combustion instability and thermal efficiency, manifesting more concentrated heat release and greater influences on the combustion duration from 10% to 50% in burned mass fraction than that of 50%–90% range. The combustion visualizations show that ignition energy mainly affects initial flame kernel formation and early flame development, and improved flame speed and combustion instability can be observed even when excess air coefficient reaches 1.4 at sufficiently high ignition energy. Furthermore, an empirical criterion based on burned mass fraction and combustion visualizations was adopted to quantify early flame development. The shortage of ignition delay time and the acceleration of initial flame propagation are observed with the increases of ignition energy, which leads to lower cyclic variations and a faster burning rate at the early combustion stage.

Speciation and Heat Release Studies during n-Heptane Oxidation in a Motored Engine

ABSTRACT The low-to-intermediate temperature oxidation of n-heptane was investigated by means of speciation and heat release analysis using a motored single-cylinder engine. The experiments were conducted under a fixed engine speed and variable compression ratios in the range of 5.0 – 7.75. A premixed fuel-air mixture corresponding to an equivalence ratio of ϕ = 0.25 was examined for stable intermediate product evolution with varying compression ratios. The experiments focus on pre-ignition species evolution and avoid explosive autoignition. The progress of reactions was followed from the onset of the low-temperature heat release (LTHR) through the negative temperature coefficient (NTC) region. A Fourier transform infrared spectrometer (FTIR) was used to detect and quantitate carbon monoxide, carbon dioxide, and n-heptane, while a gas chromatograph-mass spectrometer (GC-MS) was used to identify species that evolve between the first and second stages of ignition. A total of fifty-six stable intermediates were identified. In-cylinder pressure measurements were used to carry out a heat release analysis and correlate the global markers such as the first and second stage pressure rise to species evolution. Quantitative concentration measurements were carried out for selected alkenes, aldehydes, ketones, ethers, and alcohols. The relative experimental trend for the production of compounds within each of these chemical classes was obtained. The experimental results for speciation and heat release were compared to numerical results obtained using a detailed chemical kinetic mechanism in the literature.

Using deep neural networks to diagnose engine pre-ignition

Engine downsizing and boosting have been recognized as effective strategies for improving engine efficiency. However, operating the engines at high load promotes abnormal combustion events, such as pre-ignition and potential superknock. Currently the most effective method for detecting pre-ignition is by using in-cylinder pressure sensors that have high precision and sensitivity, but also high cost. Due to rapid advances in automotive technology such as autonomous driving, computer-aided designs and future connectivity, we propose to use a complimentary data-driven strategy for diagnosing abnormal combustion events. To this end, a data-driven diagnostics approach for pre-ignition detection with deep neural networks is proposed. The success of convolutional neural networks (CNNs) in object detection and recurrent neural networks (RNNs) in sequence forecasting inspired us to develop these models for pre-ignition detection. For a cost-effective strategy, we use data from less expensive sensors, such as lambda and low-resolution exhaust back pressure (EBP), instead of high resolution in-cylinder pressure measurements. The first deep learning model is combined with a commonly used dimensionality reduction tool–Principal Component Analysis (PCA). The second model eliminates this step and directly processes time-series data. Results indicate that the first model with reduced input dimensions, and correspondingly smaller size of the network, shows better performance in detecting pre-ignition cycles with an F1 score of 79%. Overall, the proposed deep learning approach is a promising alternative for abnormal combustion diagnostics using data from low resolution sensors.

Measurement of the instantaneous in-cylinder pressure of reciprocating compressors using the connecting rod strain

The measurement of in-cylinder pressure during operation in reciprocating compressors is usually done in a destructive test in which a small bore is machined in the side of the cylinder. This instrumentation process not only impacts the real clearance volume of the compressor but also adds undesired dynamics to the measured value. This paper proposes a novel method for pressure measurement based on the connecting rod strain which solves most of the limitations of traditional methods. Experimental results obtained with a refrigeration compressor indicate that the proposed method presents errors smaller than ±0.2 bar for a coverage probability of 95% when compared with the values measured by a reference piezoelectric pressure transducer. The results are at least equivalent to the ones presented by traditional in-cylinder pressure measurement methods, but the proposed method uses a simpler setup and does not affect the compressor working condition.

Closed Loop Control of the Combustion Phase in SI Engines Using Alternative Fuels

<div class="section abstract"><div class="htmlview paragraph">Combustion engines using alternative and/or renewable fuels are vital to reduce emission of greenhouse gases. The property of such fuels may vary significantly. The heat release rate of bio and natural gas varies of natural reasons, which is known to cause problems when used in internal combustion engines. Hydrogen is an attractive renewable fuel that has a high potential to reduce greenhouse gas emission. Bio and natural gas can be mixed with hydrogen and the content may vary depending on the availability, e.g., depending on the production from solar and wind power. Variations in the fuel property reduces the engine efficiency, unless the combustion phase is estimated and the ignition (combustion) timing is adapted to compensate for the varying fuel property. Hereby the drivability can be improved, and the fuel consumption decreased significantly, reducing the total cost of ownership and emission of greenhouse gases. However, there is not yet any widespread industrially available technique to estimate the combustion phase. In-cylinder pressure measurement is not a practical solution due to cost and life-time issues. Here, a strategy for ion current measurement signal processing is proposed as a viable alternative to in cylinder pressure sensors by estimating the peak pressure location (PPL) from the ion current. The PPL estimate meets the robustness requirements of industrial applications. The approach is described and evaluated on engine measurements. The results show that ion sense can be used for PPL estimation and the standard deviation from one estimate to another is in the order of 1-2 CAD, which can be further reduced by averaging. The PPL estimates can be used in a closed control loop to compensate the ignition timing when the fuel property varies - saving cost and reducing greenhouse gas emission.</div></div>

Investigation of cycle-to-cycle variations in a spark-ignition engine based on a machine learning analysis of the early flame kernel

High-speed Mie scatter imaging and in-cylinder pressure measurements are performed in an optically accessible four-stroke spark-ignition engine to investigate cycle-to-cycle variations (CCVs). Droplet Mie scattering is used to measure the cross-sectional flame contour. Machine learning (ML) methods are applied to predict combustion cycles of high maximum in-cylinder pressure based on flame cross-sections at -15 °CA (crank angle degrees before top dead center). All tested ML methods (decision tree-based, multi-layer perceptron, and logistic regression) are able to predict high energy engine cycles given only partial flame topology information at a temporal snapshot of the flame propagation. Feature importance analyses, employed using decision tree methods, reveal that a combination of flame position and shape features of the flames' cross-section is necessary in achieving a high prediction accuracy. These sensitivity analyses can be used to gain insight into the combustion processes and to strategically reduce the number of features. This enables the addition of new physical quantities in future investigations.

Influence of direct injection timing and mass of port injected gasoline on unregulated and nano-particle emissions from RCCI engine

The study aims to experimentally characterize the nano-particle emissions and un-regulated (i.e., saturated and unsaturated hydrocarbons and formaldehyde emissions) emissions. Present study experimentally investigates the effect of high reactivity fuel injection timings and port-injected-fuel mass on nano-particle and unregulated emissions in the gasoline-diesel RCCI engine. Additionally, empirical correlations are developed using experimental data for the estimation of particle emission characteristics. An automotive single cylinder diesel engine is modified for an in-cylinder blending of port-injection of gasoline during suction stroke and direct-injection of diesel fuel during the compression stroke. The experiments are performed on a modified engine for various diesel injection timings and port-injected gasoline mass using development electronic control unit (ECU). Nano-particle and unregulated emissions are measured using electrical mobility based particle-sizer and Fourier-transform infrared spectroscopy analyser respectively. Combustion analysis is performed by in-cylinder pressure measurement. The experimental data of nano-particle and combustion characteristics are used for the development of empirical correlation using a multivariable regression technique for determining the particle number characteristics. The parameters - premixing ratio, start of injection of diesel, and a novel parameter defined as premixed fraction of total heat release are used for the development of empirical correlations and found a good correlation for estimating the nano-particle emission characteristics. Results also indicate that advanced direct injection timing and increase in the port-injected gasoline mass leads to higher particle emissions as well as saturated, unsaturated hydrocarbon and formaldehyde emissions.

NOx, CO and HC emissions and thermodynamic-energetic efficiency of an SI gas engine powered by gases simulated from biomass gasification under different H2 content

This work explored the problem of using gaseous biofuels with different content of hydrogen and carbon monoxide in a three-cylinder naturally aspirated spark-ignition (SI) engine under laboratory conditions. The tests investigated the combustion process of simulated gases, whose composition was similar to the syngas generated from biomass gasification processes. During the lab tests, the engine operated at a constant speed and wide-open throttle. The engine control parameters and syngas composition influence on the combustion process, performance, as well as its harmful effects on the environment were analysed. The assay also focused on the fast-changing combustion parameters (heat release rate - HRR, mass fraction burned - MFB and combustion duration) based on in-cylinder pressure measurements. Gaseous fuels using during the tests were free from contamination and moisture. A clear impact of the molar fraction ratio H2/CO in the syngas mixture on the internal parameters of the tested engine could be observed. Syngas with higher hydrogen content required the use of slightly lower ignition advance to get the maximum value of Indicated Mean Effective Pressure of the engine - IMEP. The lower heating value of the syngas fuel did not directly affect the indicated efficiency of the engine. The decisive influencing factor indeed was the type and molar fraction of combustible and inert components at the syngas mixture. For syngas mixtures with higher H2 content, increasing the excess gas ratio increased the indicated efficiency. A clear correlation was found between the carbon monoxide content of the synthesis gas mixture and the specific emission of CO in the engine exhaust gas. Nevertheless, keeping the carbon monoxide content constant and increasing the hydrogen content in the syngas mixture resulted in a decrease of specific CO emissions.

Repeatability of High-Pressure Measurement in a Diesel Engine Test Bed.

This paper addresses the issue of metrological accuracy of instantaneous in-cylinder pressure measurement in a diesel engine test bed. In studies, the central unit has been the single-cylinder AVL 5402 engine. The pressure measurement was performed with a sensor designed for thermodynamic analysis, and the results were related to the crank angle, where two rotations corresponding to the four-stroke working cycle were denoted as angles between −360° and +360°. The novelty of this paper is the proposition of how to perform a type A uncertainty estimation of the in-cylinder pressure measurement and to assess its repeatability. It was demonstrated that repeatability of the measurement during the ignition process was difficult to estimate because of the phenomena that cannot ensure the repeatability conditions. To solve the problem, two methods were proposed. In one method, the pressure was measured in the subsequent cycles immediately after the ignition was turned off, and in another method, the engine was driven by a starter. The latter method provided maximal pressure values much lower than during usual tests. The obtained repeatability of measured pressure was %EV = 0.4%, which proved high capability of the evaluated measurement system.

Advances in traceable calibration of cylinder pressure transducers

Accurate and reliable dynamic pressure measurements are needed for optimizing performance in modern combustion engines, manufacturing processes and aerospace applications. Besides fast pressure transients, these applications subject dynamic pressure transducers to elevated temperatures. Both of these quantities effect the sensitivity of transducers. Therefore, transducers should be calibrated at conditions that corresponds to the operating environment.To answer these needs, the National Metrology Institute VTT MIKES has developed its drop weight dynamic pressure primary standard further. Developments include improved control and measurement of the falling weight, extension of the pressure range to combustion engine pressures down to 3 MPa and a heating option for dynamic pressure transducers under calibration. These advances enable traceable calibration of cylinder pressure transducers at conditions relevant to engine applications. The overall uncertainty (k = 2) of calibration is estimated to be around 1.7%. The performance was demonstrated by calibrating a piezoelectric pressure transducer in the pressure and temperature range from 7 MPa to 30 MPa in 20 °C, 120 °C and 180 °C, respectively. As a result, traceable calibrations of dynamic pressure transducers can be performed at conditions relevant for engine applications. This improves the reliability and accuracy of in-cylinder pressure measurements.

Experimental investigation of the influence of ignition system parameters on combustion behavior in large lean burn spark ignited gas engines

To achieve high efficiency and low pollutant emissions with large spark ignited gas engines, operation at high excess air ratios and high turbulence levels in the combustion chamber is necessary. Under these severe boundary conditions, it is a great challenge to reliably ignite the air-fuel mixture and keep cycle-to-cycle variation of the combustion process within reasonable limits. This paper investigates the influence of ignition system parameters on combustion behavior by analyzing the overall ignition and combustion process in detail: the ignition system, the electric arc, the early phase of combustion and finally the whole combustion process.Measurements were carried out on a large bore spark ignited single-cylinder research engine and on a specially designed arc test rig. In the research engine, ion current probes were applied around the spark plug in the spark plug sleeve so that a detailed analysis of the early phase of combustion was possible in order to assess the influence of ignition system parameters on combustion. In addition, crank-angle resolved in-cylinder pressure measurements provided information about the overall combustion process. The arc test rig enables the optical investigation of the influence of ignition system parameters on electric arc behavior under non-combustible atmospheres and at thermodynamic conditions and flow conditions similar to those in the research engine at spark timing. For consistency, the same modulated capacitive discharge ignition system and spark plug were installed on both test rigs. The combination of the two test setups facilitates in-depth understanding of the phenomena observed during ignition and combustion.Near the lean engine operating limit, increasing the nominal spark current duration to a certain level yielded faster combustion progress and lower cycle-to-cycle variation of the combustion process. The investigation of the early phase of combustion by means of the ion current measurements revealed the same trend: Increasing the nominal spark current duration leads to an increase in the flame front velocity during the early phase of combustion. The results from the arc test rig indicated that an increase in nominal spark current duration leads to an increase in the maximum of the cycle-averaged electric arc length. In total, the arc test rig results suggest that besides the increase in overall dissipated secondary energy, the increase in electric arc length is the second important factor in achieving the development of a stable flame kernel and a rapid combustion process in the engine when the nominal spark current duration is varied from 100 to 500 µs at very lean engine operation.

Establishing Thermal Stability in an Optically-Accessible CIDI Engine

<div class="section abstract"><div class="htmlview paragraph">Optically-accessible engines are a key tool for the study of sprays, mixing, and ignition and combustion phenomena in internal combustion (IC) engines. Due to their construction, they are typically operated for limited durations, resulting in significant thermal transients in the in-cylinder surface temperatures and cycle-to-cycle in-cylinder gas temperature. This makes collection of highly repeatable data difficult and can introduce considerable uncertainty in the in-cylinder thermal conditions. In this paper, rigorous analyses of transient in-cylinder boundary conditions and in-cylinder gas temperature were performed in an optically-accessible compression-ignition engine. Piston surface thermometry, in-cylinder pressure measurements, and in-cylinder gas thermometry were employed to determine the engine warmup time required to reach a quasi-steady thermal state for motored operation over a range of intake air temperatures and pressures from 300-420 K and 100-300 kPa, respectively. The effect of fueling on thermal stability was investigated for single-injection mixing-controlled compression-ignition combustion utilizing a range of skip-fire ratios from 5:1 to 50:1 and loads from 0.8 to 10.1 bar gross indicated mean effective pressure. Both optical and metal pistons were studied. A motored warmup time of 300 s was found to be sufficient for the engine to reach a thermally stable condition regardless of piston material or intake condition. Piston temperature was found to increase with load, but the increase was modest for even the highest load studied (~4 K) for 10 injection sets typical of late direct-injection optical engine studies.</div></div>

Portable In-Cylinder Pressure Measurement and Signal Processing System for Real-Time Combustion Analysis and Engine Control

<div class="section abstract"><div class="htmlview paragraph">This paper presents an in-cylinder pressure measurement system for cycle-to-cycle feedback combustion control purposes. Such a system uses off-the-shelf components to measure cylinder pressure and performs user-defined algorithms for heat release analysis. The working principle of the device is discussed as well as the simplifications for heat release analysis required for fast computation. The system is benchmarked against a commercially-available combustion analyzer in order to quantify the accuracy and time response. The results showed that the system is satisfactorily accurate for combustion phasing control. The main advantage, however, comes from the reduction of calculation and communication delays observed in the commercially-available system. This enables the use of cycle-to-cycle cylinder pressure-based feedback control algorithms. The functionality of such a device is demonstrated in a spark-ignition experimental engine fitted with an externally cooled exhaust gas recirculation (EGR) loop. Here, an optimal combustion phasing was the target for a feedback combustion controller that automatically adjusted the spark advance. The favorable results proved the system suitable not only for this particular combustion control problem with EGR but also for many of the modern combustion control strategies in gasoline and diesel engines.</div></div>

Exploring the lean limit operation and fuel consumption improvement of a homogeneous charge pre-chamber torch ignition system in an SI engine fueled with a gasoline-bioethanol blend

The transportation sector faces a big energy challenge as it looks for more advanced technologies and renewable sources, in which pre-chamber ignition systems and bioethanol have gained worldwide recognition. In this manuscript, a homogenous torch ignition (HTI) system was experimentally analyzed in a commercial four-cylinder engine equipped with port-fuel injection and fueled with a gasoline-bioethanol blend with 25% of bioethanol by volume (E25). Tests were performed at a wide range of speeds and loads for stoichiometric and lean mixtures. Through in-cylinder pressure measurement, a combustion analysis was carefully carried out. Results show that the HTI system leads to a much faster combustion rate and low engine cycle-to-cycle variation due to enhanced ignition energy and turbulence levels in the main chamber, and is able to extend the lean combustion limit with acceptable combustion covariance up to λ = 1.30. Moreover, improved combustion phasing combined with reduced pumping losses and lower heat transfer to the cooling system decreased fuel consumption. BSFC was improved up to 8.4%, 12.1% and 10.2% for engine speeds of 2500, 3500 and 4500 rpm, respectively, for the 3.5 and 4.6 BMEP conditions at λ = 1.20, while the higher load (5.8 bar BMEP) was improved up to 8.6% at λ = 1.30.

Pollutant emissions, performance and combustion behaviour assessment of an Si gas engine fuelled with Lcv gas containing carbon monoxide and hydrogen diluted by nitrogen

This paper includes the experimental test data of an SI engine fuelled with simulated LCV gas (Low Calorific Value), which resembles synthesis gas in composition. The LCV gas was simulated by a mixture of carbon monoxide, hydrogen and nitrogen. During the experiment, the lower heating value of the LCV gas was altered by dilution with nitrogen. A single-cylinder Honda GX270 engine was adopted in the experiment to assess the impact of LCV gas on the system performance. This engine is typically used to power various machines and for electrical energy production in small generator sets. A modified engine was connected to an electric generator, which was loaded with an electric resistor. Engine operation was controlled using a microprocessor controller. All tests were performed at constant engine speed (3000 rpm). The engine was working at wide-open throttle for all mixtures. All mixtures were burned at stoichiometric conditions and with fixed value of ignition timing (30 deg bTDC). The indicated performance of the SI engine was evaluated based on the in-cylinder pressure measurements. No significant impact on the main internal parameters of the tested SI engine fuelled with simulated LCV gas diluted by nitrogen was observed. The experimental tests showed that the combustion duration increased for the mixtures with higher content of inert gas. Increase in the LHV raised the specific emissions of NOx and decreased specific emissions of CO and HC.

Pressure Sensor Data-Driven Optimization of Combustion Phase in a Diesel Engine

In this article, a pressure sensor data-driven optimization by using extremum seeking (ES) technique is applied to optimize the combustion phase in a diesel engine. In particular, a cost function is constructed for the ES optimization with the in-cylinder maximum temperature $\hat{T}_{\text{max}_n}$ , which is an indication of NOx emission performance, and the thermal efficiency $\eta _n$ as tradeoff considerations. The data-driven nature lies in the fact that $\hat{T}_{\text{max}_n}$ is estimated from the in-cylinder pressure measurement within each engine cycle by assuming the in-cylinder process to be a quasi-steady state process, which is, then, compensated with the model-free ES optimization. It is noted that the approach developed in this article does not require the use of real NOx sensor data, which could otherwise jeopardize the ES optimization practically due to the unignorable and hard-to-predict gas transportation delay. Therefore, it is argued that this article actually delivers an alternative soft sensor solution to real NOx sensors for engine optimization purpose. The effectiveness of the proposed method is demonstrated on a single-cylinder diesel engine test bench with the help of steady-state engine tests. The method can be extended to data-driven optimization applications that also utilizes physical sensors with measurement delay.

Predictive In-Cycle Closed-Loop Combustion Control with Pilot-Main Injections

This paper studies the use of predictive in-cycle close-loop combustion control to reduce the stochastic cyclic variations of diesel combustion. The combustion metrics that fully define the pressure trace with a pilot-main injection i.e. pilot and main start of combustion, burned pilot mass, and engine load are used as the set-point reference. These metrics are in-cycle predicted by calibrated models as functions of the current cylinder state, estimated by in-cylinder pressure measurements. The proposed approach uses four individual controllers for the set-point error minimization, which respectively regulate the injection’s timing and duration of the pilot-main injection. The controllers are implemented in a FPGA and tested in a Scania D13 engine. The steady-state error reduction, disturbance rejection and transient response are discussed. The results confirm the error reduction in both, cycle-to-cycle and cylinder-to-cylinder variations. The error dispersion, measured by the 95% confidence interval, was reduced between 25% and 75% for all the controlled parameters. By on-line adaptation, the controllers are robust against model uncertainties and fuel types.

Effects of direct-injected hydrogen addition on methane combustion performance in an optical SI engine with high compression-ratio

Natural gas is one of the most potential alternative fuel of clean combustion and anti-knocking property. However, slow-burning rate and obvious cyclic variations have become the major concerns for modern gas engines. Based on a high compression-ratio, optically accessible, single-cylinder spark-ignition engine, fundamental experiments were conducted to investigate the role of direct-injected hydrogen under from stoichiometric to lean combustion conditions. Synchronization measurement of in-cylinder pressure and optical flame imaging was conducted to analyze cycle-to-cycle variations, indicated thermal efficiency, and flame evolution. The results show that as the addition of direct-injected hydrogen, the cycle-to-cycle variations decrease and indicated thermal efficiency increases, with advanced combustion phase and shortened combustion duration. The combustion imaging indicates that the significant positive influence is from the direct-injected hydrogen, which promotes initial flame kernel formation and early flame propagation. Further, an empirical criterion for mass fraction burned combined with optical data was adopted for quantification and analysis of early flame evolution. It shows that the addition of direct-injected hydrogen mainly promotes the early-stage flame propagation, manifesting increased the burning rate and thermal efficiency. The results shall give useful information in the application of direct-injected hydrogen to improve natural gas engine performance while increasing flame speed and controlling cyclic variations.

Identification of power output of diesel engine by analysis of the vibration signal

Power output is one of the main working parameters of a diesel engine, which not only reflects its dynamic performance but also acts as an important indicator of its operating state. At present, diesel engine power monitoring mainly depends on dynamometers, but most engines cannot be so equipped during operation. In addition, other techniques, such as in-cylinder pressure measurements used to gauge power output are invasive and have higher requirements for sealing and reliability. Therefore, it is important to study other means for achieving real-time monitoring of engine power that do not damage the engine. In this paper, we use the vibration acceleration of the combustion phase in the angle domain as the original signal to identify the output power. However, the signal contains many interference signals and must be pre-processed by purification techniques such as filtering, de-noising and empirical mode decomposition. Finally, the automatic identification of the power of a diesel engine is realized by means of inductive monitoring system algorithms. The test results show that the recognition accuracy under the five different working loads ranges between 83% and 95%, which demonstrates the effectiveness of the proposed method.

An experimental analysis of performance and exhaust emissions of a CRDI diesel engine operating on mixtures containing mineral and renewable components

The manuscript presents a comparative analysis of the performance and emission characteristics of a compression ignition engine equipped with a Common Rail injection system. The engine is fueled with diesel-biodiesel mixtures containing 25% and 50% share (by volume) of renewable components. Conventional diesel is used as a reference. Turkey lard and rapeseed oil are used as raw materials and subjected to the single-stage transesterification process to obtain methyl esters. The experiments are performed on a medium-duty, turbocharged, inter-cooled, Common Rail Direct Injection (CRDI) diesel engine. This study concentrates on one engine speed of 1500 rpm, typical for gen-set applications, and mid-load range from 100 Nm to 200 Nm. The scope of measurements covers the analysis of exhaust gasses concentration and engine efficiency parameters. In addition, the in-cylinder pressure measurements are performed in order to provide insight into the differences in combustion characteristics between examined fuel mixtures. The study reveals that the addition of the renewable component to fuel mixture positively affects a number of examined performance parameters as well as decreases the concentration of the examined toxic exhaust components, in the majority of cases.