Systec Automotive

Mass air flow measurement on the engine: Installation Locations, Disturbance Variables, and Typical Errors

Susanne Koerber-Wilhelm — Tue, 31 Mar 2026 09:09:03 +0000

Why the need for precise mass air flow measurement on the engine? Stricter emission standards, such as Euro 6 and 7, China 6 and 7, and Bharat 7, combined with ever-decreasing installation space, present a challenge. Engine developers of trucks, construction machinery, and agricultural machinery are familiar with this dilemma. Measuring devices on commercial vehicle engines must be precise, robust, and durable, withstanding up to 1.6 million kilometers. This article describes the locations for mass air flow measurement on the engine, environmental influences affecting accuracy, and common errors occurring during installation and operation.

Why mass air flow measurement on the engine is one of the most demanding measurement tasks

A commercial vehicle engine is not a laboratory environment. It vibrates, pulsates, and experiences temperature extremes for years on end. Precise measurements can only be obtained if the measuring principle, measuring location, and installation situation are perfectly matched. Accurate air and exhaust gas recirculation measurement — EGR measurement, for short — is the basis for complying with emission limits.

The differential pressure principle: robust, low-maintenance, and pulsation-resistant

Differential pressure measurement, or dp measurement, is proven for use on engines. A primary element in the flow path, such as a Venturi tube or a pitot tube, generates a pressure difference, proportional to the flow velocity. The sensor and evaluation electronics use this to calculate the mass flow. Since the primary element has no moving parts, the measuring principle is particularly robust against vibrations and contamination. This enables accurate mass air flow measurement over a long period of time. DP systems with sampling rates of over 2 kHz can calculate engine-related pulsations in real time.

Venturi: A nozzle with smoothly tapered inlets and outlets

dp: Differential Pressure

EGR: Exhaust Gas Recirculation

Pitot tube: a measuring device located directly in the gas flow

Inlet sections and installation space

The underestimated basis for precise mass air flow measurement on the engine

What is an inlet section, and what happens if it is too short?

The inlet section is the straight, undisturbed pipe section upstream of a measuring device where the
flow calms down. Gas that has just passed through a bend, a valve, or a turbocharger flows chaotically and asymmetrically. This leads to incorrect measurements. In the confined engine compartment, achieving
the ideal inlet section is often difficult. Flow straighteners and CFD simulations are used to optimize installation locations on a computer during the development phase.

Flow straighteners: grid-like pipe inserts that mechanically straighten the profile

CFD simulation: Computational fluid dynamics — numerical flow simulation

Locations for mass air flow measurement on the engine

Advantages and disadvantages at a glance

Several typical positions exist for mass air flow measurement on commercial engines, each with its own pros and cons.

Measuring locations in detail

1. Before the turbocharger: smooth flow and varied piping

On the intake side before the turbocharger, temperatures and pressures are moderate, and the flow is relatively smooth. However, the piping varies greatly depending on the vehicle and engine variant, making calibrating the measuring device more complex. This measurement location is particularly suitable if there is little variation in the air ducting.

2. and 3. Before and after the intercooler: Less pulsations vs. direct installation advantage

The intercooler, a heat exchanger that cools compressed air heated by the turbocharger, has a useful side effect: it dampens pulsations. This means that very accurate measurements are possible before the intercooler, even though at high temperatures. After the intercooler, low temperatures often allow for direct flange installation without additional brackets. While this saves installation space, the pulsations are particularly strong here, making signal processing more difficult.

4 and 5: Hot and cold exhaust gas recirculation (EGR): Conflict of objectives between pressure loss and EGR rate

In the EGR line, exhaust gas flows back into the intake tract to reduce nitrogen oxide (NOx) emissions. This is one of the most challenging environments for measurement technology because soot particles, oil mist, and condensates are deposited on the primary element in the cold EGR after the EGR cooler. Additionally, many measuring devices generate pressure loss in the EGR channel. That leads to reduced EGR rates and undermines the emission concept. Modern coatings on the primary element counteract this problem by reducing particle deposits and making the measuring element more resistant to aggressive exhaust gas components.

6. Exhaust System: Extreme temperatures and the strategic role of the particulate filter

Extreme conditions prevail in the exhaust system, such as those involved in controlling AdBlue injection at the SCR catalytic converter. Taking measurements after the diesel particulate filter makes sense here: The exhaust gas is largely free of particles, which greatly reduces deposits on the primary element. However, the high temperatures require temperature-resistant materials and sensors.

7. Special measuring locations: Natural gas, biogas, and fuel cells

Additional measuring locations arise in natural gas and biogas engines, as well as in multi-stage charging. For fuel cell drives, precise mass air flow measurement is essential for the efficient operation of the fuel stack.

The influence of environmental conditions on measurement accuracy

The underestimated disturbance variables

Pulsations and vibrations: pressure fluctuations as a constant challenge measurement under variable engine conditions

Pulsations caused by valve operation and the engine’s mechanical vibrations make precise mass air flow measurement on the engine difficult. These vibrations are particularly strong after the intercooler. The engine valves generate rhythmic pressure surges in the intake pipe, by opening and closing. DP flow measurement systems with pitot probes operate without moving parts. This makes them significantly more robust than devices based on other measuring principles when it comes to such influences. The evaluation electronics are also crucial; adaptive filter algorithms with high sampling rates reliably separate pulsations from actual mass flow. This works even at highly pulsating measuring points, such as after the intercooler.

Temperature extremes and density compensation: Why volume flow is not enough

Flow meters initially measure volume flow. However, what engine developers need is the mass air flow, or the weight of the gas per unit of time. Since the density of gases changes significantly with temperature and pressure, continuous density compensation based on current measured values is necessary. This issue is especially apparent in the exhaust system, where temperatures can fluctuate from below 100°C at idle to above 500°C at full load depending on the engine’s load. Therefore, integrated sensors that incorporate both into the mass air flow calculation in real time are not just an option, but a necessity.

Particles, soot, and condensates: Long-term drift due to deposits

Deposits of soot particles, oil mist, and condensates gradually alter the geometry of the primary element and, consequently, the measured value. This long-term drift is dangerous because it builds up slowly and is undetectable during commissioning. It mainly affects measuring points in the EGR line because chemically aggressive exhaust gas components, such as sulfur dioxide, nitrogen oxides, and condensed acids, are present. This requires the use of corrosion-resistant materials and protective coatings. Anti-adhesive coatings and aerodynamically optimized geometries, such as Venturi shapes, minimize the risk of deposits.

Typical sources of error during installation and operation and how to avoid them

Development and installation errors: too short inlet sections and incorrect assembly

Errors can occur at two stages: during development and during assembly. During the development phase, measurement locations are sometimes not planned with sufficient consideration of metrological requirements. For example, a lack of space can result in an inlet section that is too short. These systematic design errors affect all vehicles in a series and are difficult to correct retrospectively. Additionally, assembly errors can occur, such as an incorrectly aligned pitot tube, a flange gasket that protrudes into the cross-section, or leaky pressure hoses, which can distort the measurement on a specific vehicle.

While both types of errors rarely lead to the immediate total failure of the engine or the measuring device, they do distort the measurement. While this may not be noticeable during commissioning, it leads to permanently increased emissions and lower efficiency over the vehicle’s entire service life.

Operational drift: How measuring devices lose accuracy over time

Even correctly installed measuring devices can lose accuracy over time due to deposits on the primary element, corrosion in aggressive media, abrasive particle wear, or seals fatigued by heat, cold, or temperature changes. Therefore, measuring devices, especially those in commercial vehicle engines, must be stable in the long term. This can be achieved through the use of corrosion-resistant materials, suitable coatings, and a sensor architecture with proven zero-point stability. For reference, systec Automotive specifies an accuracy of better than 1 % at commissioning and better than 2 % over the entire vehicle life for its TFI sensor platform.

Conclusion: Precise flow measurement on the engine requires an understanding of the system. And the correct sensor.

Achieving precise mass air flow measurement on the engine involves more than just selecting the appropriate sensor. The measurement location, intake distance, robustness against environmental conditions, and careful installation must all be considered to ensure consistent, precise flow measurements. These factors are essential for efficient engine management that complies with emission standards throughout the vehicle’s whole service life.

The post Mass air flow measurement on the engine: Installation Locations, Disturbance Variables, and Typical Errors appeared first on Systec Automotive .

systec Automotive at SIAT 2026 in Pune

Susanne Koerber-Wilhelm — Fri, 02 Jan 2026 18:39:16 +0000

Measurement technology for commercial vehicle engines and more

From 28 to 30 January 2026, systec Automotive will present its latest system solutions for precise gas measurement and flow monitoring at SIAT (Symposium on International Automotive Technology), an international trade fair in Pune, India. SIAT is considered one of the most important platforms for research and technological developments in the automotive and commercial vehicle industry in Asia.

Gas volume measurement on engine and test bench

The focus of the trade fair presentation will be on TruckFlow Integrated (TFI), an air mass sensor for commercial vehicles that determines exhaust gas flows directly at the engine. TruckFlow uses the differential pressure principle and has been specially developed for the challenging conditions encountered in engines, including pulsations, temperature fluctuations, and condensates. Another advantage is that the TFI has its own integrated evaluation unit and therefore operates independently of the ECU. This means it delivers reliable measurement data throughout the entire service life of a truck, enabling manufacturers to optimise their drive systems for low emissions.

Alongside TruckFlow, systec Automotive will also present the deltaflowB differential pressure sensor, which is designed for precise flow measurements in test benches and industrial applications. Its fast response time and high stability make it an ideal tool for development and validation processes in automotive engineering.

Flow measurement for industry

systec Controls, a sister company, is complementing the trade fair presentation with further highlights from the field of flow and flow measurement. On display is the deltawaveC, a clamp-on ultrasonic flow meter for gases and liquids that leaves pipes and tubes intact. Also on display at SIAT is the deltaflow solution, which uses differential pressure to measure gas and air flows in industrial applications. At SIAT 2026, systec Automotive and systec Controls will demonstrate how suitable measurement methods, compact designs and well-thought-out operating concepts are taking flow measurement to a new level.
Visit us at SIAT 2026 in Pune to experience ‘Made in Germany’ measurement technology that combines precision, reliability, and technological expertise.

The post systec Automotive at SIAT 2026 in Pune appeared first on Systec Automotive .

Challenges and solutions in engine flow measurement

Susanne Koerber-Wilhelm — Thu, 01 Jan 2026 19:00:02 +0000

Why is flow measurement on engines so complex?

Dynamic and thermal influences on flow measurement in engines

Flow measurement in engines is one of the most challenging tasks in measurement technology. Hardly any other measuring point is influenced as much by changing operating conditions, vibrations, temperature and pressure fluctuations as the engine compartment of a commercial vehicle, be it a lorry or a construction machine. Those who require precise and stable measurements in this environment depend on robust sensor technology and stable solutions for signal evaluation.

1. Uneven gas flow

Flows in the intake or exhaust tract are rarely uniform. Pulsations caused by engine operation, valve openings or turbochargers lead to highly fluctuating volume flows. This dynamic makes it difficult to calculate an exact average value, requiring sensors for gas flow measurement that deliver stable results even under dynamic conditions.

2. Vibrations and mechanical stress

Engine vibrations directly affect the measuring elements. Without suitable damping and signal processing, this can result in noise or inaccurate readings. A solid mechanical design and intelligent signal analysis are therefore crucial.

3. Dirt, condensate and particles

Exhaust gas measurements are often impaired by soot, oil mist or condensate. These deposits can alter flow conditions or block measuring openings. Low-maintenance systems with a self-cleaning effect or an adapted probe shape minimise this influence.

4. Limited installation space and short inlet sections

Space is at a premium in the engine compartment. Flow measurement sensors on the engine often have to be mounted directly after bends, valves or turbochargers, where the flow profile is severely disturbed. In these cases, the correct inflow angle and optimal positioning of the probe are crucial.

Influence of temperature and pressure fluctuations on measurement results

Compensation and density correction of gas flow measurement under variable engine conditions

Hardly any other measurement task is so strongly influenced by thermodynamic changes. When measuring flow at the engine, pressure and temperature fluctuate constantly depending on the load. These changes directly affect the density of the medium and therefore the calculated mass flow.

Systems developed specifically for this purpose compensate for these influences through integrated pressure and temperature measurements, delivering accurate, density-compensated values even under highly fluctuating conditions.

Signal stabilisation and data processing in differential pressure measurement on the engine

A key issue in engine flow measurement is processing the differential pressure signal.

Differential pressure measurement (DP measurement) has proven to be particularly robust and reliable. It enables precise measurements even at high temperatures and with pulsating gas flows, and is also low-maintenance.

To stabilise the signal, modern dp systems use digital filters, moving averages and adaptive algorithms. This ensures that the signal remains evaluable even in the presence of high noise levels and delivers reproducible results.

Conclusion: Precise flow measurement on the engine requires an understanding of the system.

Flow measurement on the engine requires more than just installing a sensor. The influence of pressure and temperature on flow measurement is particularly relevant here. The following factors are crucial for precise measurement results:

correct positioning in the flow path
physical compensation for pressure and temperature
robust signal processing
a sensor architecture that can withstand vibrations and contamination.

It is only through the interaction of these factors that reliable, dynamically correct measured values can be achieved, both on the test bench and in real driving conditions.

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