Optimizing Carburetion in Two-Stroke Engines with the AirPro Air Densimeter

Contents:

What is Air Density
Why Measure Air Density
How to Measure Air Density
What Data is Displayed on the Densimeter
Data Storage and App Usage
A Practical Example for Rotax Engine

What is Air Density?

Air density is the mass of air contained within a specific volume. It is primarily influenced by several factors:

• Air Temperature.
• Atmospheric Pressure.
• Humidity.

The higher the density, the more oxygen is available for combustion. In motorsport, especially with two-stroke engines, accurately knowing the air density is crucial for achieving maximum and reliable performance.

Air density is critically important: without this value, engine carburation cannot be precisely adjusted. In particular, it is essential to monitor changes in air density throughout the day to correct the carburation and optimize it for that specific moment.

Why Measure Air Density and How It Affects Two-Stroke Engines

In two-stroke engines, carburation must always be calculated based on the actual amount of oxygen present in the intake air. The key is the air-fuel mixture introduced into the cylinder. Consequently, it is vital to monitor the air, as its density determines the correct ratio of oxygen to fuel.

If the air is denser (on cold, dry days), a richer jetting is needed to ensure the right amount of fuel. Conversely, when the air is warm and humid, its density decreases, and the carburation tends to become richer due to the lower amount of oxygen. Sub-optimal carburation leads to poor engine performance and, in the worst cases, can cause seizures or engine damage.

Of course, the optimal range, represented by the green zone in the graph, can vary in high-performance 2T engines depending on the desired operating range. What's important to highlight is how the stoichiometric ratio changes with Air Density.

How to Measure Air Density

Our AirPro densimeter is a compact and precise instrument designed to measure air density in real-time. Thanks to its integrated Temperature, Pressure, and Humidity sensors, it automatically calculates the density and displays it instantly. This provides a clear and constant reference for adjusting carburation, without relying on rough estimates or guesswork.

To get the best results from the AirPro Densimeter, place the device in a well-ventilated area. Once you've found the optimal spot, leave the instrument until it reaches the same temperature as the surrounding environment.

What Data is Displayed on the AirPro Densimeter?

Let's analyze the data shown on the densimeter's display in the photo above.

• 15:10:08 - Time. It's always recommended to keep the time updated so that when you save sessions, you have a precise time reference for the measurement.
• 20.5°C - Air Temperature. You can set the unit of measurement to °C or °F via the APP.
• PRESSURE = 1014.2 - Atmospheric Pressure in hPa.
• rH% = 54.5 - Relative Humidity.
• AIR DENS = 1.197 - Air density value in Kg/m³. You can set the air density to Kg/m³ or Lb/Ft³.
• % = 97.7 - This is the air density percentage relative to the standard value of 1.225 Kg/m³. A value below 100% indicates less dense air than standard, while a value above 100% indicates denser air (and therefore richer in oxygen).
• ALT = -7.2 mt. Relative Altitude value. You can set the unit of measurement to meters (mt) or feet (ft). In warm, humid air, density is lower → the device shows a higher relative altitude. In cold, dry air, density is higher → the device shows a lower relative altitude.
  

Please note that the relative altitude value shown by our instrument does not reflect your actual geographical altitude. Instead, it represents a calculated value based on air density, often referred to as "density altitude." This value indicates the theoretical altitude at which the same air density would be observed under standard atmospheric conditions.

Data Storage and App Usage

By simply pressing one of the two MEM buttons, the values on the display are stored in the device. You can store up to 50 sessions in the internal memory and download and view the data on the Prisma Electronics APP.

Each session will be saved to the track where you are located, making it easy and quick to find all sessions for that location. Using the notes field, Engine Tuning #1 in the photo, you can write down your personal notes to track any changes made. You can also export individual sessions as a PDF to share with a team member via WhatsApp, for example, and also in EXCEL format.

A Practical Example: The Jetting Calculator for Rotax Engines

To make using the densimeter even easier, we have developed a small calculation tool for Rotax engines. By entering the air density value measured by the AirPro, the system automatically suggests the most suitable carburetor jet for the current atmospheric conditions. This helps reduce setup time and ensures maximum engine efficiency, both on the track and in races.

Of course, the absolute jet size depends on many factors, such as the driver's style, the mechanical grip on the track, and the target RPM range. Our jetting calculator for Rotax engines helps you understand how carburation changes under different atmospheric conditions.

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