Can I Modify a 200 kVA Diesel Generator to CNG Gas?

It is certainly possible to convert a 200 kVA diesel generator to operate on Compressed Natural Gas (CNG) instead. However, the feasibility and cost-effectiveness of such a conversion depend on various factors, including your technical skills and knowledge. The process can also vary significantly in cost compared to purchasing a new CNG generator.

Conversion Considerations

When considering the conversion of a diesel generator to run on CNG, it is essential to understand that a perfect 100% conversion to natural gas is not feasible or practical. The efficiency and performance of such a system are limited by the characteristics of both fuels and engine requirements.

Realistic Options

Buying a Complete Replacement Gas Engine: This is often the most straightforward and reliable option, though it will come with a higher cost due to the complete replacement of the generator unit. Bi-Fuel Products: These systems involve a mixture of CNG and diesel fuel. Bi-fuel generators allow natural gas to be mixed with the induction air, increasing the calorific value of the fuel mixture. This allows the diesel fuel pump to reduce the fuel input while maintaining the generator's output. Typically, such systems substitute approximately 85% of diesel with CNG, but the exact percentage may vary depending on the application and operational conditions. The Pilot Fuel Method: In this method, the diesel generator retains its diesel fuel supply as a pilot fuel. The diesel engine is designed to run at a slightly lower speed with no electrical load. CNG is then introduced into the intake system with a governor-controlled mechanism. This setup can be either a modification of the original governor or the addition of a new electromechanical governor tailored to the specific generator. This method involves less complexity compared to bi-fuel systems but may result in reduced output. Additional Fuel Linkage: Another approach involves connecting a linkage to the injector rack, which adds CNG as the diesel fuel injection increases. This configuration provides more power without risking detonation, although it may lead to a higher diesel fuel consumption.

Easiest Method: Retaining Diesel as a Pilot Fuel

The easiest and most cost-effective method is to retain diesel as a pilot fuel. The diesel generator’s governor is disconnected, and the injector rack is fixed to maintain the generator's operation at a slightly lower speed than the design speed. CNG is then fed into the intake system using a governor-controlled mechanism, either modified or new.

Steps Involved:

Remove or disable the carburetor. Install a governor-controlled CNG injection system, either an existing one or a new electromechanical governor. Ensure the lean NG/air mixture avoids detonation and ignites with the pilot charge of diesel fuel. Monitor and adjust the NG flow to avoid detonation, which may limit obtainable output.

BNSF attempted this method on several train locomotives with mixed results. Although the performance was impressive, the complex logistics of LNG fuel handling made it less practical compared to other methods.

Alternative Conversion to Spark Ignition

Converting a diesel generator to a spark-ignition system involves a more substantial and complex modification, making it a less common and more involved process. This method requires changes to the engine's ignition system and may not be suitable unless the generator's existing systems can be adapted with significant modifications.

Conclusion

While converting a 200 kVA diesel generator to CNG is possible, the choice of method depends on your technical proficiency and the specific needs of your application. Bi-fuel systems and the pilot fuel method are often more practical and cost-effective options compared to a complete engine replacement. Proper planning and execution will ensure that the generator operates efficiently and reliably with CNG as the alternative fuel source.