Technical Paper: Digital Combination Sensor

The TRICAN sensor supports two-way-communication for system level plausibility diagnostic with another external sensor. Its digital output as per J1939, CAN2.0 can be configured to customer needs (CAN Frame).

TRICAN delivers relative humidity, specific humidity and dew point if requested. It also measures air temperature and intake pressure as shown in figure 4.

• Relative humidity (RH) is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature.
• Specific humidity (Sh) is the ratio of the mass of water vapor to the total mass of the moist air parcel.
• Dew Point (DP) is the temperature to which the air must be cooled to become saturated with water vapor. When further cooled it will condense to form liquid water.

TE’s humidity cell is a unique high-performance sensor in terms of accuracy, robustness, response and recovery times. A thin dielectric polymer is trapped between an upper and lower electrode. The dielectric capacity is proportional to the measured humidity. Its position on the sensor allows for quick recovery time after condensation and strong protection against pollutants at the same time. Our humidity sensor offers one of the lowest hysteresis and fastest response time on the market today.

TE’s pressure sensor is developed especially for ICT air intake. Its operating temperature range is from -40°C to +125°C and offers a pressure range up to 250kPa with very quick time response.

The temperature sensor is a negative temperature coefficient (NTC) soldered on the PCBA. It offers a temperature measurement range from -40°C to 105°C with an accuracy of ±0.5 °C.

Humidity is known to affect air intake density thus affecting combustion [3, 4]. EGR loop adds humidity to the air intake. Humidity, temperature and pressure sensors allow for performance enhancement and fuel consumption optimization. It offers the following advantages:

• Injection adaptation
• Ignition timing adaptation
• Monitoring of EGR condensation to prevent from cylinder lifetime reduction
• NOx emissions reduction
• EGR loop control optimization

In natural gas engines, maximum achievable power is a function of air intake humidity. An accurate air/fuel ratio in lean-burn engines is essential.

The excess of air reduces combustion temperature thus nitrogen oxide emissions reduced by half compared to a conventional NG engine. With the excess of oxygen, the combustion is more efficient because more power is produced from the same amount of fuel.

Lean-burn limit is a function of humidity and must be adapted in real-time to:

• Improve efficiency
• Reduce NOx emissions, knock & misfire

Virtual NOx estimation allows for high cost reduction due to the removal of the upstream NOx sensor. One of the major advantages is that the TRICAN accuracy is high even at cold start conditions where 50% of the driving cycle’s emissions are generated during cold start where NOx sensors are not efficient for at least 20 minutes. In these specific conditions, emissions are the highest and require a specific strategy.

In addition, temperature and pressure sensors at the intake can be replaced by the TRICAN allowing additional cost reduction.

Our humidity, pressure and temperature sensor completes or replaces upstream NOx sensors. It offers high accuracy, high reliability and limited drift over its lifetime. It is also used in an engine model in combination with upstream NOx sensor to offer system diagnostic capability and to monitor NOx accuracy over lifetime.

Optimum fuel cell performance requires High relative humidity or nearly saturated humidity (Rh>80%) is required to fuel cell performance. Proton Exchange Membrane permeability depends on its water content; therefore, relative humidity is one of the most important operation conditions affecting fuel cell performance and efficiency over the stack’s lifetime. 

A humidifier is used at the inlet of the fuel cell to correct humidity rate. One of the main challenges for the sensor is at cold start when condensation can occur. Field experience in harsh environments such as trucks, construction machines and on/off-road applications where TE’s humidity cell is used, have proven to be a reliable solution which offers fast recovery time after condensation and high response time. Pressure is also a key parameter for power density control. The TRICAN sensor is thereby suitable for high humidity and temperature environments.  Additionally, the sensing elements are protected against chemical contamination.

Due to combustion speed reduction, cylinder max pressure decreases when specific humidity increases. As shown in figure 9, engine torque decreases by 5.5% when specific humidity increases from 10 to 40g/kg due to max pressure reduction. For conditions where specific humidity is 15 g/kg, if the measurement varies by 5g/kg, engine torque will drop by 1%.

Hydrocarbon emissions arise from unburned particles due to wall extinction phenomena. They increase when air humidity increases, while carbon dioxide and nitrogen oxide decrease when air humidity increases.

For conditions where specific humidity is 15 g/kg, and the measurement varies by 5g/kg, the emissions impact is: 1.5% more hydrocarbons, 7.2% more nitrogen oxide, and 5.4% more carbon dioxide.

Adiabatic end-of-combustion temperature affects the amount of heat released during combustion and thus the work done by the piston which affects engine power.