Combustion Engine Analysis and Setup in DewesoftX

Course overview

This course provides a deep dive into engines’ thermodynamic and dynamic behaviors using DewesoftX. You’ll start by covering the fundamentals: piston-driven energy conversion, differences between spark-ignition and diesel cycles, and how the CEA module integrates engine data acquisition—combining cylinder pressure and crank-angle information to derive combustion metrics.

Through practical setup lessons, you’ll configure analog pressure channels and high-resolution angle sensors (e.g., encoder, CDM), then set up the CEA plugin. This includes entering cylinder count, stroke type, stroke geometry, and ignition timing. You’ll apply signal filtering and mapping functions to align measurements accurately across engine cycles.

Next, the training focuses on result calculations: extracting peak pressures, crank-angle positions of pressure peaks, heat-release curves, and polytropic coefficients. You’ll also learn how to detect knocking events using a high-pass filter (5–12 kHz) and knock-factor logic, which helps differentiate true knock from background noise by comparing filtered signals within reference and knock-specific angle windows.

Advanced modules cover combustion noise analysis—converting spike-filtered pressure to sound-level metrics—and the use of statistical functions for cycle-by-cycle trend monitoring and optimizing engine performance. You’ll practice exporting results, including P–V plots, heat-release data, TDC offsets, and knock logs. Finally, the course shows how to integrate CEA data with other Dewesoft modules—like CAN bus, video sync, GPS, and ECU data—for a complete engine test setup.

By the end of the course, you’ll be able to accurately acquire, analyze, and interpret combustion data with DewesoftX—improving engine design, optimizing performance, and diagnosing combustion-related issues.

The high-accuracy combustion analyzer system from Dewesoft is used for engine research, development, optimization, and testing of ignition systems, exhaust systems, and valve control mechanisms.

Internal combustion refers to the process of burning fuel inside the engine. In a car engine, gasoline is burned internally, releasing energy that powers the vehicle. Other types of internal combustion include diesel engines and gas turbine engines. Internal combustion is an efficient system that requires a relatively small engine to generate motion. It is also more fuel-efficient than external combustion engines, such as traditional steam engines.

Gasoline engines were once as inefficient as steam engines. The gasoline engine, invented in 1876, was initially no more efficient than a steam engine, wasting significant amounts of fuel. In 1878, Rudolph Diesel set out to develop a more efficient engine, and in 1892, the diesel engine was born. While more efficient as an internal combustion engine, early diesel engines were noisy and produced sooty exhaust, initially limiting their use to trucks. Modern advancements in internal combustion have made diesel engines cleaner, quieter, and more efficient. The primary difference between gasoline and diesel engines lies in how fuel is converted into energy.

Turbines are another method for generating power through rotational motion. Examples include wind turbines, steam turbines, water turbines, and gas turbines. Gas turbines operate on the principle of internal combustion. In a modern gas turbine engine, fuel combustion produces pressurized gas, which expands rapidly, creating a high-speed blast of hot air that spins the turbine. Propane, natural gas, kerosene, or jet fuel can be used in these engines to generate energy.

An internal combustion engine (ICE) is a heat engine in which the combustion of fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an ICE, the expansion of high-temperature, high-pressure gases produced by combustion applies direct force to a component of the engine. This force is typically applied to pistons, turbine blades, a rotor, or a nozzle. The movement of these components over a distance transforms chemical energy into useful mechanical energy.

The first commercially successful internal combustion engine was developed by Étienne Lenoir around 1859, and the first modern internal combustion engine was created in 1876 by Nikolaus Otto.

The term "internal combustion engine" usually refers to engines with intermittent combustion, such as the more familiar four-stroke and two-stroke piston engines, along with variants like the six-stroke piston engine and the Wankel rotary engine. A second class of internal combustion engines uses continuous combustion, including gas turbines, jet engines, and most rocket engines, all of which operate on the same basic principle. Firearms can also be considered a form of internal combustion engine.

In contrast, external combustion engines, such as steam or Stirling engines, transfer energy to a working fluid that is not mixed with, contaminated by, or consisting of combustion products. Working fluids can include air, hot water, pressurized water, or even liquid sodium, typically heated in a boiler. ICEs are usually powered by energy-dense fuels, such as gasoline or diesel, which are liquids derived from fossil fuels. While stationary applications exist, most ICEs are used in mobile applications and are the dominant power source for vehicles such as cars, aircraft, and boats.

Typically, an ICE is fueled with fossil fuels like natural gas or petroleum-derived products such as gasoline, diesel fuel, or fuel oil. There is a growing use of renewable fuels, including biodiesel for compression-ignition engines and bioethanol or methanol for spark-ignition engines. Hydrogen is also occasionally used and can be obtained from either fossil fuels or renewable energy sources.

Diagram showing the operation of a 4-stroke spark-ignited engine. Labels:
1 – Induction
2 – Compression
3 – Power
4 – Exhaust

• Intake, Induction, or Suction:
  The intake valves open as a result of the cam lobe pressing down on the valve stem. The piston moves downward, increasing the volume of the combustion chamber and allowing air to enter in the case of a compression-ignited (CI) engine, or an air-fuel mixture in the case of spark-ignited (SI) engines that do not use direct injection. In both cases, the air or air-fuel mixture is referred to as the charge.

• Compression:
  During this stroke, both valves are closed, and the piston moves upward, reducing the combustion chamber volume, which reaches its minimum when the piston is at TDC (top dead center). The piston performs work on the charge as it is compressed, increasing its pressure, temperature, and density. This behavior can be approximated using the ideal gas law. Just before the piston reaches TDC, ignition begins. In an SI engine, the spark plug receives a high-voltage pulse that generates a spark, igniting the charge. In a CI engine, the fuel injector sprays fuel into the combustion chamber, where it ignites due to the high temperature.

• Power or Working Stroke:
  The pressure of the combustion gases pushes the piston downward, generating more work than was required to compress the charge. Complementary to the compression stroke, the combustion gases expand, causing their temperature, pressure, and density to decrease. When the piston approaches BDC (bottom dead center), the exhaust valve opens. The gases expand irreversibly due to the leftover pressure exceeding the back pressure (gauge pressure at the exhaust port); this process is called the blow-down.

• Exhaust:
  The exhaust valve remains open while the piston moves upward, expelling the combustion gases. In naturally aspirated engines, a small portion of the combustion gases may remain in the cylinder during normal operation, as the piston does not completely close the combustion chamber. These residual gases mix with the next charge. At the end of this stroke, the exhaust valve closes, the intake valve opens, and the cycle repeats. The intake valve may open slightly before the exhaust valve closes to improve scavenging.

The DewesoftX  Combustion Analysis math module enables the analysis of internal combustion engines. By measuring the pressure inside the cylinder and the shaft angle, we can calculate key engine indication values for development and testing, such as maximum pressure, the position of maximum pressure, heat release, knocking, and other important parameters.

The combustion analysis is fully integrated within the Dewesoft X software, allowing the use of any Dewesoft functionality, including CAN bus, video, analog signal acquisition, and more.

The video below demonstrates how quick and easy it is to set up combustion analysis in Dewesoft and begin measurements.

SIRIUS Combustion Analyser data acquisition systems are used for engine research, development, and optimization. They are also employed for component development and testing, including ignition systems, exhaust systems, and valve control gear. The system consists of our top-notch isolated SIRIUSi hardware and the well-known DewesoftX software package for measurement and analysis.

It supports angle- and time-based measurement results and uses highly sophisticated algorithms for online or offline mathematical and statistical calculations of heat release and other thermodynamic parameters.

The combustion analyzer can be fully integrated within a testbed and also supports data from other sources, such as video, CAN, and Ethernet. If the powerful integrated post-processing features of DewesoftX are insufficient, the data can also be exported to multiple file formats.

In addition to combustion analysis, the system can be expanded to handle other measurement applications, such as hybrid testing of the powertrain, noise and vibration measurement, and synchronized video or GPS data.

DAQ system overview

Pressure sensor(s) are used to measure the cylinder pressure of the engine. Depending on the sensor type, they can be connected directly to a SIRIUSi amplifier like any other input channel, or through external signal conditioning amplifiers. Charge-type sensors can be connected directly to CHG amplifiers.

Additionally, an angle sensor is required to obtain angle-domain measurement results. Several types of angle sensors are supported by the Dewesoft Combustion Analyser. Additional mounted CDM (Crank Disc Marker) sensors or digital native CDM sensors (such as 60-2 or 37-1) with TTL outputs can be connected to dedicated counter inputs.

Sensors with analog output can:

• Be connected directly to analog input channels,

• Or connected to counter inputs via the DS-TACHO device.

In both cases, the DewesoftX re-sampling technology provides an angle resolution down to 0.1°.

Like many other modules, Combustion Engine Analysis is also available as an option in the standard DewesoftX package. To add the module, simply go to the Channel setup tab, click More, and select Combustion Engine Analysis.

The basic settings for the CEA module must be configured here as well. Before adding the module, you can click the screwdriver icon to the right of the Combustion Engine Analysis option to access the CEA settings. If the module has already been added, simply open the general Settings, select the Extensions tab, and locate the CEA module in the tree window. A preview of the CEA settings is shown in Image 5.

CEA Settings:

• The Check Encoder Pulses setting for the encoder limit is only used in real angle domain acquisition and is therefore not needed for Dewesoft’s Combustion Engine Analyzer.

• If Scope Mode is enabled, CEA skips cycles—in other words, it does not calculate all cycles. Several levels of scope mode are available. Depending on this setting, the CEA module may also skip calculations based on the measurement mode (storing, not storing, trigger, etc.).

• The default setting, which should be used for CEA to calculate, store, and visualize all cycles, is: Never.

• Engine templates (e.g., calculation methods) are stored in the engine templates path.

• Limit the maximum number of cylinders on generated display applies only to the preview of an automatically generated measurement display.

The Combustion Engine Analyzer in DewesoftX is just one of several application modules that offer dedicated mathematics and specialized visual controls, such as the p-V diagram and the CEA Scope.

Since the analog channels of the SIRIUS system serve as the input for mathematical calculations, you must first set up the amplifier and configure the scaling for the physical units. This is done in the Analog section of the setup screen.

Once you are satisfied with the analog configuration, you can proceed to the next step and use these analog channels as inputs for the CEA module.

You can use the same analog input channels that you have used in the Combustion Engine Analyzer module for any other mathematics or applications (e.g., FFT) in parallel. This provides a multi-functional instrument suitable for nearly any application. Moreover, output channels from one mathematics module can be used as input channels for any other module.

The correct hardware should be selected based on the type of engine application. If a very low-RPM engine is being used and charge-type pressure sensors are required, a SIRIUS device with charge inputs should be chosen. Alternatively, DSI-CHG adapters can also be used, but they do not offer the same filter settings as charge inputs. In the images above, a clear difference can be seen between the lowest high-pass filter setting on a SIRIUS with CHG inputs (Image 9) and a DEWE-43 with a DSI-CHG-50 adapter (Image 8).

Signal noise should always be minimized through proper cabling and correct mounting of the pressure sensor. If unwanted noise remains in the pressure signal, filtering can be applied to reduce it.

High-pass filter

For a low-RPM engine, the high-pass filter should not be set too high.

Low-pass filter

For a high-RPM engine, the low-pass filter should not be set too low.

You must configure the Combustion Engine Analyzer (CEA) module after setting up the analog input channels.

The configuration of the CEA module is divided into three sections:

1. Engine settings: Defines the geometry of the engine and assigns channels to the cylinders.

2. Encoder settings: Assigns the encoder or angle sensor, sets the resolution, and configures TDC detection.

3. Result definition: Enables or disables different calculations and determines the output channels for the CEA module.

Basic parameters

Volume per cylinder

In the Volume per Cylinder field, the Volume Source must first be defined. This determines the geometry of a cylinder, which can be one of the following:

• written in manually - Geometry option,

• imported curve as a Text file or 

• defined within the selected Engine template.

Selected cylinder settings

For each cylinder, Selected Cylinder Settings can be applied, allowing you to configure Cylinder Deactivation, Zero Level Correction, and Additional Channels. This is done by clicking the Settings button in the Cylinder Overview for the desired cylinder, as shown in Image 18.

Zero level correction

Dewesoft CEA supports three different correction principles:

Additional channels

Additional channels can be applied to each cylinder. These channels are aligned with the corresponding cylinder and will be available in the CEA-Scope diagram. They, like the pressure channels, are also recalculated to the angle domain. For example, you can apply the injection or ignition signal to display it together with the pressure signal.

Signals for additional channels do not need to be limited to analog signals; they can also come from other modules. For instance, torsional vibration outputs can be added to CEA to view the results in the engine’s angle domain.

For example, if an injection signal is applied and the number of injections (events) is set to 3, with the start trigger level set to 2 V and the end trigger level set to 1 V, each time the signal crosses 2 V, the corresponding angle position related to the cylinder where it is applied will be recorded [deg]. The same applies to the end of the event: when the signal crosses 1 V (negative edge), the position will be recorded [deg].

In a real measurement, you can set trigger level values based on a simple pre-measurement: start the measurement in Measure mode and observe the signal values for each injection channel. Then return to the CEA setup and enter those values in the trigger level fields.

Cylinder overview

For each cylinder, the corresponding pressure channel needs to be assigned from the channel input list. Additionally, the ignition misalignment relative to the reference cylinder must be entered in degrees.

The sampling type of the Dewesoft CEA is always time-domain. This has the advantage that all time-domain functions are not influenced by changes in the sample rate due to shaft speed and remain consistent. For example, a power calculation works only in the time domain (with a fixed sampling rate).

Of course, CEA calculations are still performed in the angle domain, so the time-domain data are always recalculated into the angle domain.

The required computational power for recalculating time-based signals into the angle domain is distributed across all available CPU cores of your PC.

Angle sensor setup is performed in the Encoder Settings tab, as shown in Image 22.

Sensor types and angle resolution

Nearly any angle sensor type is supported. To establish a relation to a fixed angle position, the sensor must provide a fixed angle mark. The drop-down list automatically displays all suitable sensor types from the counter database, as shown in Image 23.

To add a new counter sensor, click Options → Editors → Counter Sensors, and you will enter the Counter Sensors editor, as shown in the image below.

After selecting the sensor type, we need to define where the sensor is connected.

Under Properties, the fine adjustment for the angle sensor must be performed. In the case of analog sensor selection, the trigger levels can be precisely adjusted. First, the trigger edge is defined according to the signal. Then, the trigger and retrigger levels are set. It is recommended to use the retrigger level to avoid false triggers, as they can disrupt CEA operation and result in incorrect angle information.

Retrigger: After a trigger occurs, the signal must cross the retrigger level to arm the trigger again. This prevents noise around the trigger from causing false triggers.

Under Properties, the fine adjustment of the angle sensor must be performed. For analog sensor selection, the trigger levels can be precisely adjusted. First, the trigger edge is defined based on the signal. Next, the trigger and retrigger levels are set. It is recommended to use the retrigger level to prevent false triggers, as they can disrupt CEA operation and produce incorrect angle information.

Retrigger: After a trigger occurs, the signal must cross the retrigger level to rearm the trigger. This ensures that noise around the trigger does not cause false activations.

The next step is to define the target angle resolution for the combustion analysis calculations. The upper frequency is limited by the selected resolution and by the dynamic acquisition rate set in the analog channel configuration.

TDC detection

Top dead center (TDC) detection is used to shift the reference cylinder pressure to 0° (deg). The offset between the angle sensor zero and the TDC position of the reference cylinder is called the trigger offset. This value can be entered manually or measured automatically.

Image 29 shows the angle offset of a non-fired (cranked) engine.

For automatic TDC detection (Start button), the number of cycles must be entered. CEA will automatically measure the average offset over the specified set of cycles. The maximum pressure typically occurs before the actual TDC of the piston due to thermodynamic losses and blow-by. Therefore, the measured value is corrected using the thermodynamic loss angle.

After TDC detection is complete, the average value—including the thermodynamic loss angle—will be automatically set as the trigger offset.

The example above used the installed pressure sensor to measure the TDC. This is a very convenient and fast method. The only variable is the thermodynamic loss angle.

Instead of a pressure sensor, a TDC sensor can be used. The TDC sensor must be connected to an analog input and assigned to the reference cylinder in the CEA setup. The thermodynamic loss angle should be set to 0, and automatic TDC detection can then be started again. After the measurement, the pressure channel must be configured in the CEA setup.

There are numerous options available in the Result definition for CEA within Dewesoft X, as shown in Image 32. A detailed overview of the channels and their descriptions can be found in the Combustion analyzer manual, Chapter 7.3, Channel Overview on page 25.

For each group name—Acquired Signal and Standard Calculations—different values can be used for calculations, and various types of averaging can be enabled:

In the Result Definition section from the previous chapter, "How to Define the Results?", it was shown that there are numerous calculations that can be applied as results. The following section introduces all the calculations that can be used within Dewesoft X.

The Group Name column in the Result Definition tab (see Image 32) is divided into three groups:

• Acquired Signals, which are, by default, selected as “used” for calculation

• Standard Calculations, which are entirely optional for result definition.

• Two-stroke calculations, which are available only when a two-stroke engine is selected in the engine settings.

There are two types of thermodynamic calculations that can be used.

Thermodynamics 1 is the basic thermodynamic calculation implemented in the first CEA module and was available in previous versions of Dewesoft X. It is now primarily used for comparison purposes when referencing older results.

Thermodynamics 2 is an upgraded and advanced thermodynamic calculation algorithm and is currently the primary tool for such calculations in Dewesoft X.

Thermodynamics 2 and temperature calculations are closely related. Therefore, when clicking the Thermodynamics 2 Setup button, the settings for temperature calculation will also appear, as shown in image 37.

There are a few settings that can be defined in Thermodynamics 2 and the Temperature result definition:

Thermodynamics 2 defines the pressure derivative along with the heat release:

• Temperature:

For the Pressure Derivative, the start angle, stop angle, and step size must be defined.

The Start of Combustion (SOC), End of Combustion (EOC), and the Mass Fraction Burned (MFB) points I5, I10, I50, I90, and IXX (user-defined point) are calculated if heat release is activated.

Depending on the fuel type (Diesel or Gasoline) selected in the engine setup, SOC is defined differently (refer to the manual, Chapter 4.1, Engine Setup, page 9):

• Gasoline: SOC is defined where MFB = 5%.

• Diesel: SOC is defined where MFB crosses 0%.

The burned mass fraction is calculated from the integrated heat release, TI. The maximum of the integrated heat release corresponds to 100%, and the angle positions for I5% to I90% are extracted.

Theory of knocking

Knocking is an uncontrolled combustion of fuel in engines. During normal operation, the fuel-air mixture is ignited by the spark plug (in gasoline engines) and burns smoothly. When the engine experiences knocking, self-ignition occurs at the outer edges of the combustion chamber, causing high-pressure transients that can overload the engine both mechanically and thermally. This can severely damage engine components, particularly the piston.

The knock detection algorithm identifies knocking so that the user can respond to this abnormal condition. Knocking can be detected by extracting the high-frequency components from the cylinder pressure signal using a high-pass filter. The typical knocking frequencies range between 5 kHz and 12 kHz.

The high-pass (HP) filter (red line in Image 38) extracts frequency components above the cut-off frequency.

Compared to Image 39, pressure fluctuations can be observed on the falling slope of the pressure curve (blue). The combustion pressure curve can reach very high pressures—often exceeding 100 bar—making it sometimes difficult to observe these fluctuations on top of the main combustion curve. By extracting only the high-frequency components above 5000 Hz, knocking can be analyzed more easily. The high-pass filtered pressure signal (red line) highlights the pressure fluctuations around the peak of the pressure curve.

Another important value is the maximum pressure of the high-pass filtered signal (red), which can be extracted and visualized on a recorder display, immediately reflecting the pressure transients of previous cycles. This value is a good indication of knocking, but under certain circumstances, it may provide inaccurate information. If the pressure curve is very noisy or if a spike caused by an external electrical signal is present, the maximum value extracted from the high-pass filtered signal may appear elevated, even though it is not related to knocking.

Knocking typically starts at the pressure maximum and continues along the falling slope of the pressure signal. Instead of taking only a single value (the peak), we can integrate the high-pass filtered signal over the negative part of the pressure slope. This integrated value (knock integral, KI) provides a more stable measure, reducing the impact of single transient noise peaks.

The high-pass filter outputs absolute pressure values (positive values only). Therefore, when we integrate the signal, we can suppress individual transients, but the integration will also include any persistent noise. Depending on the engine speed, this noise may increase, which in turn raises the integrated signal. With a single integration, it can be difficult to distinguish between actual knocking and simple noise.

To prevent this, the integration can also be performed before the point of maximum pressure, allowing for a comparison of results before and after the peak.

Knock Factor (KF) provides a weighted measure related to knocking. When no knocking is present, the KF is approximately 1. The integration windows (reference window and knock window) are separated at the average position of maximum pressure.

The example in Image 43 shows the pressure curve (blue) and the high-pass filtered signal (red) in the top diagram. The diagram also highlights the maximum pressure extracted from the high-pass filtered signal (red) and the calculated KF (orange). Both maximum graphs exhibit peaks, indicating that knocking is present and can be detected, provided that no spikes are present.

A few cycles earlier, an error spike can be seen (red curve in Image 44). Although the maximum of the filtered signal still exhibits a peak here, the KF algorithm does not indicate any knocking, and the resulting value is close to 1.

This way DewesoftX can provide robust knock detection, even in the presence of accidental spikes in the signal. The example in Image 44 shows a very noisy pressure signal. The KF (orange) remains around 1 because the integrated noise is similar in both the reference (green) window and the knock (red) window.

Set up the knock detection algorithm (Mannesmann VDO AG)

The previous chapters have described the signals that can be obtained from the knock detection algorithm:

• High-pass filtered pressure signal

• Maximum value of the high-pass filtered pressure signal

• Knock factor

In Image 46, the settings for the knock detection calculation are shown.

Low-pass filter

The reference window and the knock window are separated at the maximum pressure point (red curve), without being affected by noise or pre-existing knocking peaks. A running average filter is used here, with the number of taps corresponding to the angular resolution. If the CA angle is set to 0.2° and 40 taps are used, the resulting moving average window (smoothing) is 40 × 0.2° = 8°.

From the filtered (smoothed) curve, the maximum pressure position determines the separation between the knock and reference windows.

• Recommended value [deg]: 4–10°. Info: TAPS = deg / angle resolution

High-pass filter

Here, the high-pass filter frequency is set in Hz. The pressure curve is high-pass filtered (blue), and the result can be displayed in the CA-Scope. The channel is named CylinderChannelname/KnockHP.

Recommended value [Hz]: 5000 Hz

Noise threshold

For the Knock Factor, the quotient of the integrated signal of the Knock window and the Reference window is calculated. If the pressure value is lower than the specified threshold, the threshold value will be used for integration. This approach reduces the influence of varying base noise levels between the Reference window and the Knock window.

Recommended value [bar]: 0.1–0.5 bar

Reference, Knock signal window width

The width of the Reference window and the Knock window is defined here. It is recommended to set both windows to the same length, so that the noise threshold is at a reasonable level and the KF value is approximately 1 when no knocking is present. If the window sizes are set differently, the base value without knocking becomes the quotient of the two window lengths.

Shift reference window

At higher RPM, knocking can sometimes begin before the maximum pressure. In this case, part of the knock signal may fall into the Reference window, which reduces the Knock Factor (KF) value. To prevent this, the Knock window and the Reference window can be shifted according to the actual engine speed.

With the above settings, the window is shifted at 6000 RPM by 10° CA (or 5° CA at 3500 RPM). If any knocking occurs before the maximum pressure point, the KF reading will not increase, as no knocking leaks into the Reference window when the windows are shifted correctly.

Background information about the High-pass filter:

The cylinder pressure channel is already available as an angle-domain result, meaning the time between samples varies with the engine speed. Since the high-pass filter cut-off frequency must be set in Hertz, a conventional IIR filter would not work.

The high-pass filter is created from a moving average window with a specific width, which is subtracted from the original signal. As with all filters, a minimum sampling rate is required for the filter to operate properly.

With the high-pass filter set to 5000 Hz, a sampling rate of at least 22,500 Hz is required. With an angle resolution of 0.1° (3600 pulses per revolution), a minimum engine speed of 375 RPM is needed to achieve this sampling rate.

The table below shows the minimum engine speed depending on the angle resolution and a set high-pass (HP) filter of 5000 Hz.

The channel names are continuously created as default names by the CEA Math module. They can also be changed afterward by accessing the channel or sub-channel list, as shown in Image 52. Some default names can even be customized by modifying the engine template. For further information, please refer to the Combustion analyzer manual, Chapter 8: Customizing the CA-Module, on page 71.

The CEA module of Dewesoft X calculates all relevant results for combustion analysis, as described. However, some applications or measurements require advanced calculations that are not directly supported within the application’s Mathematics module. In these cases, the complete Mathematics toolbox of Dewesoft X can be used to obtain the desired results.

This chapter explains the Combustion Noise feature and provides a brief overview of the associated statistics.

Theory of combustion noise

Combustion Noise measurement is used to calculate external noise from an internal combustion engine using cylinder pressure. In other words, the cylinder pressure (combustion event) generates external noise.

The CEA Noise must be calculated in the time domain. First, the value is scaled from bar to Pascal. This is followed by the U-filter, which simulates the engine transfer function (1st and 2nd filters in the overview). Optionally, the A-filter (human hearing filter) can be applied to determine the perceived noise produced by the engine.

Setup of combustion noise

The formula for converting Pascal to dB is:

Depending on the configuration, each input channel can produce up to three output channels:

• Weighted Raw: The result is a time-domain signal with the U-filter and optional A-filter applied, converted to Pascal (if the input unit is bar). This result can be further analyzed using the Sound Level Meter.

• Overall Value: The result of CA Noise over the entire measurement, expressed in dB. At the end of the measurement, a single value is obtained and stored.

• Interval Value: The CA Noise is calculated over specified intervals. It is recommended to set the interval to include at least 1 or 2 engine cycles. Only the lowest RPM needs to be considered. For example, at 600 RPM (10 Hz = 100 ms), an interval of at least 0.2 s should be set for a 4-stroke engine to obtain stable results.

Basic statistics setup

If further statistical calculations are required, we can use the Basic Statistics function in Dewesoft X. This can be added via the Math module → Add Math → Add Basic Statistics. A screen similar to the one shown in Image 55 should appear.

Input defines the channels from which the statistics are calculated. Since the CA module generates many output channels, the channel filter function helps locate the required channels.

Several results can be defined under the Output Channel section. For each input, the corresponding result is calculated. In the Output section, you will see a list of all calculated channels. You can, for example, change the default channel names.

There are several ways to define the time interval for the calculation as well as the time interval for the resulting output.

Basic statistics of angle domain data

The example settings in Image 56 are based on cycle-based data, producing one value per cycle. Basic statistics can also be calculated from angle-based data—for example, the maximum pressure curve over a defined number of cycles.

For both angle-domain and cycle-based data, the same setup can be used. The only difference is that the output channels of angle-based statistics are vector channels. In the bottom-left corner of the screen, you can see different previews depending on the data type: cycle-based channels display a single value, while angle-domain channels display a data curve (vector channel).

Different input channel types can also be mixed in a single statistics module: time-domain, angle-domain, or cycle-based data. The statistics module will always use the correct output channel type corresponding to each input data type.

Array statistics

For analyzing angle-domain data, the array statistics function can be used. Array statistics can be added in the Math module → Add Math → Add Basic Statistics. A screen similar to the one shown in Image 58 should appear.

This module only accepts input channels of vector type (angle-domain data). The output is always a single value calculated for each vector. Therefore, when using array statistics on CEA data, the result is always a cycle-based value.

Array mathematics

Another powerful tool for manipulating data from the CEA module is array mathematics within the Formula setup. Only array (or vector) data are allowed as input channels, making this function suitable for angle-domain data from the CA module.

It can be added via Math module → Add Math → Add Formula.

Using the functions min, max, and avg, we have the same functionality as array statistics. Additionally, individual data points of an array can be accessed using [ ] or { }.

The formula shown in Image 58 subtracts the value at -30° from the vector:

1'PCyl2'-'PCyl1'{30}

In other words, the additional CA channel is offset-compensated using the value at -30°.

It is also possible to extract a portion of an array:

1'PCyl2'{-30:60}

As a result, we will obtain a new array containing data from -30° to +60°.

Automatic display mode

When you start the measurement, Dewesoft X will automatically generate a display setup (also called a measurement screen) named CEA, which shows the major signals for a quick start. The tooth wheel symbol on the CEA display icon indicates that this display has been automatically generated. In Image 60, the automatic display configuration is shown. The orange square visual control is a 2D diagram that can be assigned to an angle-based result channel.

The handling of all visual controls follows the same concept. For the selected visual control, the properties are displayed on the left side, while the channel selector for that visual is shown on the right side. Only channel types suitable for the selected visual are available. For example, you cannot select statistic channels for a visual control that expects angle-based data. Channels that are currently selected are shown in bold.

Customizing displays

DewesoftX allows full customization of the measurement screens; that is, you can add, remove, and rearrange all visual controls to suit your specific needs. The major visual controls for combustion analyzer measurements are described below.

Overview of data types

Not every display can handle every data type. Different input data sources generate different data types, and different mathematical functions generate different data types as well. Moreover, the result of a mathematical function may also depend on the input channel type.

For example, the CEA module uses time-domain data as input and primarily generates:

• Angle-domain data aligned to the combustion cycle, and

• Cycle-based data, which holds one value per cycle.

Below is a summary of the different data types, including examples of sources and which visual controls can be used for each type.

Scalar (single data points)

Scalar channels contain a single value per time slot (in contrast to vector or array channels, which contain multiple data values per time slot). Depending on how they are acquired or calculated, these channels can be divided into three groups:

• Synchronous

• Asynchronous

• Single value

The most common channels are synchronous channels, which are usually analog, counter, or digital input channels, as well as simple mathematical operations based on these channels. Synchronous channels are time-domain data with equidistant intervals between samples. The sample interval is defined by the dynamic sample rate (except for external clocking).

Asynchronous channels include, for example, CAN bus or GPS data. Mathematical functions can also result in asynchronous channels. Examples include:

• The result of block-based mathematics, such as statistics output

• All cycle-based data from the CEA module (e.g., MEPx or MaxPressure)

Single value channels contain only one value per measurement. Examples include:

• Constants, such as header variables

• The output of mathematics such as:

  • Overall statistic calculations from the CEA module

  • Basic statistics

For all of these scalar channels, various visual controls are available in DewesoftX. Examples include digital meters, recorders, analog meters, bar graphs, and so on. XY recorders can also be used to visualize this data.

Vector or array channels

In contrast to scalar data channels, vector channels (also called array channels) contain multiple data points for each time slot.

Examples:

• One FFT shot consists of multiple amplitude values—one for each frequency of the FFT resolution.

• Angle-domain pressure is stored as vector data; for each vector, we obtain all pressure values over the defined angle resolution.

2D Graphs

2D graphs are designed to display these data types. Some specialized 2D graphs are dedicated to CEA:

• Combustion Scope

• PV Graph

3D Graphs

3D graphs allow you to display the history of these data channels, with time represented as the third dimension.

Matrix channels

Matrix channels are multidimensional vector channels. For example, in a 2-dimensional matrix channel, each time slot contains an array, and the elements of this array are themselves arrays (containing the data within the array elements).

The output of complex sensors, such as a thermo-camera, is a matrix. This data can be visualized in a 3D graph.

CEA-scope

The CEA Scope can be used for all angle-based data from the CEA mathematics module. Results can be displayed from actual data, running averages, overall averages, or additional channels.

Combustion PV-graph

The p-V graph (Pressure over Volume) can display both actual and averaged pressure data.

Standard display types

Cycle-based results, such as MaxPressure, are calculated for every cycle. For four-stroke engines, we obtain a single value every two revolutions, while for two-stroke engines, we get one value per revolution.

Cycle-based results can be displayed in various visualizations. The most common displays for cycle-based results are: Digital, Analog, Bar, and Recorder.

You have several options for starting and stopping data storage:

• Manually

• Automatically, using various trigger condition settings

Manual start-stop storing

If you want to manually start or stop storing, select Storing type: Always fast. The storing settings can be found under: Measure → Ch. setup → Storing.

You can start storing data directly in the setup screen by pressing Store, or you can first go to Measure to view the live data and then begin storing whenever you prefer.

To stop storing, simply press the Stop button.

Pressing Pause will temporarily stop data storage. While in pause mode, you have two options:

• Press Resume to continue storing.

• Press Stop to end the measurement and close the data file.

When you stop the measurement, the overall statistical values are stored in the data file. The illustration below highlights this difference more clearly. In the graph, you can see two marked ranges:

• Stored data time: This is the period from when the Store button is pressed until the Pause button is pressed.

• Average calculation time: This is the entire time span shown in the graph. After pressing Pause, the measurement continues (and statistics are still calculated), but the measurement data is no longer stored in the data file. However, when you press Stop at the end, the statistical values are written to the data file.

The overall averaged result (green channel: Cyl/Ave/P1/MaxP) does not match the expected average of the data values (blue channel: P1MaxP) within the Stored data time range, because the calculation continued after pressing the Pause button.

 When you open the data file in Analyse mode, the recorder will contain only the data from the Stored data time range, and the average value will not match the expected result, since the average is calculated from the start of storing until the stop.

When reloading this data file, it may appear that the average calculation is incorrect, because the complete data set used for the calculation is no longer visible. To correct this, you can recalculate the full CEA mathematics from the stored data file.

Press Offline Math, open the CEA module setup, and change the module’s calculation state from Calculated to Offline.

Go back to Review and select Recalculate to run the CEA mathematics again. The overall averaged pressure channel will now match the stored pressure data. Press Save to overwrite the original stored CEA data in this data file.

Storing a defined number of cycles

DewesoftX provides various trigger conditions for starting and stopping data acquisition. If you want to store a fixed number of cycles, you can use the Stop storing after XXX CEA cycles feature. In the example below, storing stops automatically after 100 cycles.

Start-stop on channel condition

The purpose of triggered storing is to record data based on external events. Both the start and stop triggers can be assigned to any channel. Additionally, you can define pre-trigger and post-trigger times.

DewesoftX provides various trigger conditions for starting and stopping data acquisition. As described in the chapter Manual Start-Stop Storing, it is important to consider the calculation method of the overall statistical values to ensure accurate results.

For triggered start and stop storing, you must select the Storing type: Fast on trigger. This setting allows you to define both Start storing and Stop storing conditions.

Let’s consider an example where storing should start if the maximum pressure exceeds 100 bar and should stop after 100 cycles.

The Start storing condition type is set as a simple edge on the channel P1/MaxP.

The Stop storing condition is based on the Cycle count channel. As the Mode, select Delta amplitude to stop storing after 100 cycles.

This setup already works (for example, it stores only the data of the 100 cycles), but we also need to consider the overall statistics. With the current settings, the data file remains open after the 100 cycles, and the overall statistics continue to run.

To prevent this, we can enable “Stop storing after 1 trigger.” This setting ensures that storing stops after 100 cycles, and the DewesoftX data file closes while still containing the overall statistics for those 100 cycles. When the next trigger occurs, a completely new data file is created.

With these settings, the average channels reset at the start (ARM) of the measurement. As a result, the average channels include the cycle value before the trigger event occurs. If average values are required for further analysis, they must be recalculated in post-processing, as previously described.

In Analysis mode of Dewesoft X, you can load a data file and:

• review the data,

• modify or add math modules, and

• print the complete screen to generate a report.

For analyzing recorded cycles, the yellow cursor can be moved to browse through the cycles.

Similar to Measurement mode, you can modify or add new Visual Controls or Displays. All these modifications can be saved to the data file using Save file changes.

You can also load the measurement screen layout and formulas from another data file with Load display and offline math.

By pressing Edit in the top-right corner, a context menu opens. This menu allows you to copy either the image or the data shown on the display to the clipboard or to a file.

If further analysis is needed, various data export formats are supported.

Time-domain data

When opening a Combustion Analyzer data file, the default Export Properties setting is Combustion data. To export in the time domain, the export properties must be set to Full speed data in the Data presentation option. This ensures that time-domain data is exported.

Angle-based data from the CEA module is exported as a vector (if the target export format supports vectors). These data are time-stamped at the end of the cycle time, which is also true for all cycle-based results.

The Channel list provides a quick overview of the channel type (dimension) and update rate (values per second).

Angle-domain data

To export angle-domain data, the Data presentation option must be set to CEA data. With this setting, all output channels from the CEA module can be exported as angle-domain data.

The results can be categorized into four groups:

1. Cycle data as Vector: Angle-domain data such as pressure, integrated heat release, and additional channels.

2. Averaged Cycle data as Vector: One angle vector for the complete measurement, such as the average pressure.

3. Once-per-Cycle data as Scalar: Cycle-based data such as maximum pressure (value and position), I50, and MEP values.

4. Averaged Cycle data as Scalar: One value for the complete measurement, such as the average of maximum pressure.

Before exporting the data, the x-axis base must be defined

The table below provides an overview of the differences in x-scaling when using the different export types:

File replay

It is possible to export analog channels into a file that can later be used to simulate analog channels without requiring any hardware connection. For example, if an analog angle sensor signal has been recorded, it can be exported together with the pressure signal channel(s) to simulate a running engine.

First, the extension for replay file export must be added. This extension can be found in the Download area.

Afterward, extract the file to: <Dewesoft_installation_path>\Bin\Addons\

The next step is to run Dewesoft as an administrator in order to register the extension.

Any recorded data file containing analog inputs can be exported.

In the file export process, first select the Data presentation option and choose the Full speed data type. Then select the Replay (*.rpl) export format. You can use the channel filter to locate and export all analog (AI) channels. Synchronous mathematics channels can also be exported, and they will behave like analog channels during file replay.

CAN interface

The Dewesoft Combustion Engine Analyzer can acquire and transmit CAN messages. When transmission is enabled, any measurement result can be sent to another host system (for example, INCA).

1. Add a transmit channel by pressing the +Tx button in the CAN tab.

1. You can define the CAN identifier (arbitration), its name, and the DLC (Data Length Code).

2. Define the channel types within the identifier using the following parameters: Data Format, Data Type, Start Bit, Length, and Scaling.

3. Define a transmit event for this CAN message:

• Periodic: The interval time can be set in milliseconds.

• OnButton: A control button in Measurement Mode can be assigned to this event.

• OnStart: Defines the event when switching to Measurement Mode, with a configurable delay in milliseconds.

• OnStop: Triggered when the measurement is stopped.

• OnTrigger: A measurement channel condition defines when the data should be sent.

• BeforeMessage: This message is sent before another selected message.

• AfterMessage: This message is sent after another selected message.

1. Select the data to be transmitted. You can choose either constant values or any measurement channel.

2. All defined transmit channels can be exported to a DBC file for later import into the host system.

The average delay time for CAN Out data is approximately 100 ms because the complete cycle must first be acquired, and only after calculation is the data available for output.

Testbed

Communication with the testbed server is implemented through a dedicated plug-in. You can choose between the following protocols:

• AK Protocol

• Puma Open AK

• D2T AK

• Tornado AK

For all of these protocols, either an RS232 or TCP/IP connection can be used.

Detailed information about plug-in usage and setup can be found in the Combustion Engine Analyzer Manual, Chapter 9.

In Dewesoft, the file replay option can be used to simulate analog input channels, create a CA setup, and test the functionality of CA.

First, the extension for replay file export must be added. This extension can be found in the download area.

Afterward, extract the file to:Dewesoft_installation_path>\Bin\Addons\

The next step is to run Dewesoft as an administrator to register the extension. When Dewesoft starts, open Settings to configure file replay and switch Dewesoft X to Offline mode. Then click on Simulated devices and set the Simulated channels mode to File replay (see Image 85).

An exported .rpl file can be used, or you can download a test file. Once a file is selected, information will be displayed about how many channels are simulated, the sample rate, and the total length of the file. The replay file is always in the time domain.

Select the Repeat option to loop the file; otherwise, it will be played only once. Only analog synchronous channels will be replayed.

After that, close Settings and create a new setup.

In Channel Setup, you will see nine simulated analog channels. To identify these channels, simply enable all of them and switch to Measure.

On the recorder display, all nine channels can be viewed at once. The data can also be frozen, and a specific section can be zoomed in for closer inspection. From this, it becomes clear that the first channel is the angle sensor, while the other eight channels are pressure signals. In this case, the angle sensor is a 60-2 sensor.

The channels can be renamed for easier setup, physical quantities can be selected, and scaling can be defined. In this example, a four-cylinder CEA setup will be created.

Now we need to add the CEA module.

In the Engine Settings of the CEA module, first define the cylinder count, enter the engine’s geometrical data, specify the fuel type, select the appropriate pressure signal for each cylinder, and input the ignition misalignment. After entering all the information, the engine can be saved as a new template.

The final step is to define the angle sensor setup.

In the next tab of the CEA setup, select the angle sensor type as 60-2 and specify the channel it is connected to. You should immediately see data appear on the p-V preview diagram (left) as well as the pressure signal in the angle domain (right).

If the angle sensor is defined correctly, the output on the right should display a stable and accurate RPM along with 60 pulses per revolution.

We can see that the peak pressure in cylinder 1 is around 100°CA. This indicates an offset in the angle sensor. If we had a replay file from a non-firing engine, we could perform TDC detection. However, since this file includes combustion, the offset must be entered manually. In this case, the offset is known to be 80°.

When the trigger offset is correct, the pressure curve is shifted into the proper position, and the p-V diagram displays the correct output.

If we switch to the Result Definition tab, the rate of heat release and the accumulated heat release are immediately visible.

Now we can switch to Measure, and on the predefined CEA measurement screen, all the basic combustion analysis information will already be available, as shown in Image 93.

CEA can also be used in combination with other modules. When applied to a four-stroke engine, it allows data to be reviewed in the angle domain for a complete engine cycle (720°).

This is particularly useful for analyzing vibration data in a four-stroke engine. Otherwise, the data would only be visible over a 360° cycle, as shown in Image 94.

The following is just one example of how CA can be used for other purposes, such as converting time-domain data into angle-domain data. Only one angle sensor, valid for CA, and a single input are required. The input can be of any type—an analog input, a math channel, or even an output channel from another module (e.g., torsional vibration, power analysis, order tracking, or modal testing).

Torsional vibration & combustion engine aalysis

Please refer to the ProTraining materials for a detailed explanation of the Rotational and Torsional Vibration module.

To use the vibration analysis module together with CAA, only one angle sensor is required. First, add the Torsional Vibration module.

The sensor input and sensor type must be selected, and the rotational angle must also be defined for output.

If another sensor is mounted on the opposite side of the engine shaft, the additional sensor can also be selected, and the output calculation for the torsional vibration angle can be activated.

The CEA module must also be added, and the angle sensor input configured.

In the Encoder Settings, only the pressure sensor needs to be selected—in this case, Encoder-1024—along with the counter location to which the encoder is connected.

Under Additional Channels in Engine Settings, select the output from the torsional vibration module. All additional channels will be displayed in the angle domain. If an encoder is also mounted on the opposite side of the shaft and torsional vibration results are available, additional channels can be added. All three outputs can then be selected for conversion into the angle domain (see Image 98).

When entering Measure mode and enabling Design mode, two additional display types from CAA become available. A Combustion Scope can be added to display the data in the angle domain for a complete engine cycle.

All three vibration channels can be displayed simultaneously on the graph. Pressure channels or other channels can also be added.