An investigation of diesel engine exhaust gas emissions measurement techniques and determining the optimum method

Caterpillar Inc. is the world’s largest manufacturer of earthmoving machinery, as well as trucks, tractors, graders, scrapers, excavators and much of the other machinery used in the mining, construction and forestry industries. Ammonia (NH₃) is one of the emissions released from diesel engine exhausts; however, to date, there is no strict regulation by the Environmental Protection Agency (EPA) of the amount of NH₃ that can be released from a diesel engine exhaust pipe. Only European regulation has suggested that NH₃ must be limited to 10 ppm for every tail pipe cycle (EU Commission, 2017). However, Caterpillar still have difficulty taking accurate NH₃ measurements from diesel engine exhaust pipes due to the highly reactive NH₃ making it difficult to measure, as well as the many kinds of gas analysers existing in the market having different specification and characteristics. This is a problem which other companies also face. Therefore, the main purpose of this research is to investigate and help Caterpillar Inc. select the best way to measure NH₃ from diesel engines, including comparing a number of different gas analysers and understanding the effect of the laboratory setup. In addition NO_X measurements are also included in these experiments.A literature review is initially conducted in order to learn about the various analysers, then understand the principles of each analyser and to evaluate any related previous studies. Following this, 6 projects were completed in this research and either have been published already or have been submitted and are under review as conference and journal papers. Seven different gas analysers were used in this research into measurement of NH₃; 3 different types of FTIR (Fourier Transform Infrared), 2 different types of TDL (Tuneable Diode Laser), a QCL (Quantum Cascade Laser) and an NH₃ sensor.Project 1 compared two different FTIRs having different sampling characteristics and showed that these characteristics can have an impact on the reported NH₃ measurement. This was followed by project 2 which compared a TDL and an FTIR gas analysers which showed both gas analysers have a good agreement for NH₃ measurement. Project 3 investigated the effect of the settings in the TDL conditioning box software on the NH₃ measurement, in which the results showed the software setting has a huge impact on the measurement capability of gas analysers. Project 4 compared the characteristics of the gas analyser of two different FTIRs and a QCL, again showing an impact on NH₃ measurement, whilst also the QCL was confirmed as being good for NH₃ measurement. Project 5 was the main project for this EngD research because it compared all seven different gas analysers; 3 different types of FTIR, 2 different types of TDL, a QCL and a NH3 sensor. It also investigated the way to improve the measurement accuracy of each gas analyser in which the results showed that each gas analyser with a good specification can produce good NH₃ measurements so long as the gas analysers have been maintained properly. In Project 6, a new type of experimental set-up was devised to determine the performance of the gas analysers on NH3 measurements from a diesel engine exhaust pipe. The tests were done with the QCL and the results showed that without proper maintenance, the QCL does not perform well on NH₃ measurements.The outcome of this research has helped Caterpillar Inc. to acknowledge the best way to measure NH₃ from diesel engine exhausts, best method of determining performance evaluation, as well as helping to choose the best gas analysers for NH₃ measurement. The research outcome has also helped Caterpillar Inc. to make a decision in selecting the best gas analyser system for NH₃ measurement for the Caterpillar Inc. engine manufacturer in China. The project has also had an impact on one of the gas analyser manufacturers as they have to re?examine and redesign their gas analyser due to it not being able to perform well on NH₃ measurement continually without frequent cleaning.