Investigation into Engine Wear Map Development with
Inclusive Dates: 07/01/14 – Current
Background — Stoichiometric natural gas engines are becoming more widely used in on-highway transport applications. With reduced natural gas prices, fleet operators may find a move from diesel fuel to natural gas advantageous. Compressed natural gas is a cheaper alternative to diesel and a more energy dense fuel on a mass basis. With U.S. national averages for diesel and compressed natural gas around $3.89 per gallon and $2.11 per diesel gallon equivalent, the upfront vehicle premium of the natural gas fueled engine can be regained in fuel costs. With radioactive tracer testing, there exist a means of quickly evaluating wear rates in these new powertrain units. Developing a test method for engine wear rate mapping will afford SwRI the opportunity to respond to a growing product segment through efficient, short-duration wear testing.
To evaluate long-term durability using currently available methods would require multiple engines to be run over some designed test cycle for hundreds of hours, followed by a complete engine teardown with post-test part metrology to determine the wear incurred on the critical engine parts over the operational period. Even with the current number of manufacturers producing stoichiometric natural gas engines for on-highway usage, a proven method and equipment capable of mapping wear severity across the operating range is a marketable technology.
Approach — The goal of the project is to create a wear map for the Cummins ISX 12G, with the steady-state wear rates collected through a 25-point run matrix across the operating range of the engine. To achieve this goal, a two-stage approach has been outlined utilizing a Plint Te-77 reciprocating, sliding contact tribometer prior to full-scale engine testing. Tribometer testing allows for the systematic separation and combination of operating inputs that affect part wear rates. Results from the Te-77 tribometer work will be applied to construct a method for gathering and interpreting wear rates in the fired engine testing such that the normalized steady-state wear rate observed at one set of conditions is repeatable regardless of the preceding engine condition or day acquired. The Te-77 will be adapted for use with a gamma ray detector intended to monitor the accumulation of radioactive markers in the system while the rig is operational. The inclusion of the gamma detector in the system permits monitoring the wear rate response of the parts while altering single inputs such as the applied load and/or reciprocating speed.
Through the simplified loading of ring segments running on liner segments in the Te-77 rig, the project will examine the repeatability of wear rates on single sets of test pieces across varied but controlled and repeatable parameters such as load, speed, lubricating oil flow rate, and lubricating oil temperature. Additional sets of parts will duplicate run conditions to observe the repeatability of wear rates between separate part sets.
Accomplishments — The work within the current project will result in experimental data that defines an operational and statistical approach to engine wear rate mapping. SwRI is currently working on several natural gas engine projects, and has several proposals or pre-proposals for natural gas engine design and development. The market for natural gas on-highway engines, and thus for their design and development, has been expanding rapidly for the past few years. The knowledge and experience obtained from this testing will support current and future natural gas engine projects. There is a potential for intellectual property for predicting high wear operating conditions and subsequent control strategies or features to avoid those conditions.
The project offers other significant benefits to include:
- Developing real-time radioactive wear testing on a Te-77 reciprocating test rig. Figures 1 and 2 depict the tribometer reservoir setup for tracer sampling.
- Investigating correlation between a Te-77 wear test rig and an operating engine.
- Demonstrating the use of radioactive tracer wear testing on a stoichiometric spark-ignited natural gas engine.
- Developing a test methodology to evaluate wear measurement across a range of operating conditions and under a continually changing engine "state-of-wear."