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Analyzing gas quality with CAN

In this article, Patrice Flot from CMR, considers further sensor technology in the wake of the increasing specification of gas engines for power generation. Those sensors provide measurement data to the engine via CAN.

Patrice Flot, chief technical officer at CMR, considers further sensor technology in the wake of the increasing specification of gas engines for power generation (Source: CMR)

“We are seeing gas engines more and more specified for electricity generation among a wide variety of applications as the technology continues to develop, and operators recognize the efficiency and fuel optimization advantages offered”, said Flot. “The gas engine market is expected to grow by almost 6 % in the next five years, fueled by lower gas prices, which have declined by more than 30 % in the past few years, and increased demand for power generation. Indeed, the global market for gas engines is expected to be worth USD 4,76 billion by 2022.”

“However, while the growth of gas engine usage and the interconnection of the gas networks, together with a greater requirement for reliability and availability and lower maintenance, are creating new challenges, the issue of gas quality variation - how gas quality varies between sources, countries, regulations, and even time - remains a critical factor, presenting a challenge that new sensor technology can help to overcome”, he added.

Attempts to harmonize gas quality regulations in the EU which in turn, eases gas trading across borders, are convincing gas distributors to push for a broadening of gas quality limits to enlarge the portfolio of possible sources. Simultaneously, OEM (original equipment manufacturers) engine builders, and other gas-fuel users, are pressing for restrictive limits that are better suited for their power plants and ancillary equipment.

The sensor series Niris (Source: CMR)

Natural gas is a generic designation for various qualities of gas based on the main gas component methane (CH4). As such, it covers many different qualities linked to the gas composition including the source of raw gas and refinery processes. The gas can be manufactured from synthesis technologies, natural processes, or renewable power-to-gas technologies.

Gas networks are interconnected and linked to multiple sources. Because of this, the quality of gas can change at a given location and these changes could be rapid when switching from one source to another. As well, rapid changes of gas quality can occur in other situations faced by end users, such as onsite switching from a gas tank to the gas network, or vice-versa. Also, when gas is only available in LNG tanks, switching from an empty tank to a full one can result in changes in gas quality - an empty tank will deliver the heaviest molecules contained in natural gas, and a full one may deliver the lightest molecules.

Another difficulty for builders of stationary gas engines is the rate of change of gas quality over short periods of time. Because that point is not addressed by regulation, they must cope with potential sudden changes in gas quality that are not always managed by current combustion control loop technologies. These control loops are based downward on combustion parameters measurement, not upfront on gas quality measurement.

Developments and CAN

For this purpose, the Near Infrared Intelligent Sensor natural gas sensor (Niris NG) for instance - which has been designed to analyze the natural gas composition at the inlet of the gas engine, from CMR has been developed.

The author added: “This generation of gas pipe plugged sensors use low cost optical components and proprietary signal treatment software contained within robust housing to resist vibration and heat. Light is emitted by the sensor and travels through the gas inside the supply pipe on the engine before being analyzed by a detector.” The output signal from the detector is a spectrum that is then processed by a calculation matrix to provide gas composition, and related parameters.

This matrix is specific to each sensor and is inbuilt during manufacturing at the calibration stage due to data base of gas mixtures. Calculation is carried out through multivariable methods like the principal component regression (PCR) and partial least square regression (PLS). Measurement data is then provided through a CAN protocol to the engine. The methane number input at the ECU (electronic control unit) can be used by the engine builder for the spark ignition timing and other engine actuators.

The sensors come with real-time measurement of fuel quality. Directly connected to the gas feeder pipeline, the sensor is built around infrared hardware and data treatment software and features a CAN network communications facility, which enables it to be upgradeable without dismantling the sensor for performance and retro applications. Natural gas consumption levels can be further reduced by engine tuning closer to knocking limits due to fuel management strategies using sensor data, said Patrice Flot.

Linked to electrical actuators, the generation of sensors permit adjustment of the engine during a change of gas supply from one source to another of different quality. Moreover, with the capabilities offered by a time sensor, gas authorities and suppliers can harmonize gas quality better, finding ways for agreement and opportunities for global gas trading.

2019, the company already introduced the gas sensors at the Cimac congress (the CAN Newsletter reported).


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