Patent Application
20140165954
This invention relates to testing internal combustion engines (and other piston engines), and more particularly to sampling fluid from the top land crevice of a piston.
Crevices in the combustion chambers of piston engines are of interest to researchers for many reasons. As one example, combustion chamber crevices in internal combustion engines are significant contributors of hydrocarbon (HC) emissions. These crevices are identified as narrow regions of the combustion chamber into which the combustion flame does not reach. One such crevice is the gap between the piston and the cylinder wall. During the compression stroke, unburned charge is pushed into this crevice. The crevice is narrow enough to quench the flame front, leaving unburnt gases, so that during the power stroke, as the piston descends and the exhaust valve opens, these unburnt gases re-emerge in the exhaust.
To successfully achieve emissions goals, engine design and operation must account for the effects of combustion chamber crevices. To this end, efforts have been made to sample material in the piston crevices. Past sampling methods involve drawing the sample out through tubing connected to a hole through the piston near the piston rings. The tubing traverses the connecting rod and is carried by a specially designed linkage to the point where it exits the crankcase.
A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:
The following description is directed to sampling the fluid that collects in piston top land crevices of reciprocating engines. Interest in this topic has increased in recent years due to low speed pre-ignition problems common in high-BMEP gasoline engines. Past sampling methods have been unsuccessful in collecting and preserving a volume of fluid large enough to fully understand the composition of the crevice fluid.
The system and method described herein are particularly suitable for sampling piston crevices of internal combustion engines, but would be suitable for other piston engines. The method may be performed while the engine is in normal operation. The sampling system and method are particularly compatible with automotive engine architecture, but can be used with any piston engine of any thermodynamic cycle or fuel type.
A passage 29 through the cylinder wall 23 provides access into the top land crevice 21 for the sampling device described below. The cylinder “wall” may be the engine block or engine block with a cylinder liner.
Referring to both
Tubing 300, which may be of any suitable material and is typically flexible, provides a leak-proof fluid communication into the passage. Tubing 300 first carries sampled fluid to a small in-line relief valve 301 near the combustion chamber. Relief valve 301 is set by spring preload to open near top-dead-center of the piston's compression stroke (TDCc).
Relief valve 301 determines the beginning of each sample event; its opening pressure is set to the compression pressure near TDC. It is positioned as close as possible to the cylinder, to limit additional clearance volume (and hence effect on cylinder performance) when not sampling. In other words, the length of tubing 300 between the crevice 21 and relief valve 301 is short.
Downstream from relief valve 301, connected to a second end of the tubing, is a piloted check valve (pilot-to-open) 303, which is used to stop the flow from the piston crevice 21 at some higher pressure. The pilot pressure supplied to the piloted check valve 303 is chosen so that the “micro-sample” flows into sample chamber 320 and valve 303 is closed before combustion causes a sharp rise in cylinder pressure. This avoids the introduction of large amounts of high temperature combustion gases into the closed volume of sample chamber 320. The pilot pressure is supplied with a control gas via a solenoid valve 305.
When valve 303 is open, the sampled fluid flows via sample line 307 into sample chamber 320. The micro-sample event is repeated a desired number of times until the pilot pressure to the piloted check valve 303 is reduced and the system stops sampling. Typically, the micro-sample event is repeated several times.
In this manner, a pilot pressure setting used to control the end of each micro-sample event. The pilot valve 303 closes off fluid flow from the piston crevice 21 when pilot pressure is removed.
Using these valves 301 and 303, a “micro-sample” event occurs near TDCc. Valve 301 opens at near TDCc to allow fluid flow from the top land crevice into tubing 300 toward valve 303. Valve 303 stops the fluid flow from the crevice at a predetermined pressure which corresponds to the time when combustion in the chamber causes a sharp rise in cylinder pressure. Otherwise, valve 303 is open and allows flow of the sampled fluid into the sample chamber.
After the piloted check valve 303 is closed, the engine is able to operate basically unaffected by the sampling system. Pressure builds in the space between the relief valve 301 and the piloted check valve 303 until the micro relief valve 301 does not open. The engine is then able to run as it would normally, with no appreciable clearance volume added, and hence with minimal effect on the engine's compression ratio.
After relief valve 301 closes after a combustion event, check valve 303 may be opened until it is closed during the next sample event as described above. After a number of micro samples are collected into sample chamber 320, the gas portion of the sample can be vented off using solenoid valve 309. The gas is vented from sample chamber 320 via a vent line 310 and a check valve 311.
An inert flush gas from a source 312 is used to fill the sample chamber 320 via a flush line 313 and check valve 314. This flush gas function provides sample purity.
The flush gas then drives the fluid sample from the sample chamber 320 a gas chromatograph 330 (or other analysis equipment) after trapped combustion gases are vented. The flush gas may also be used to purge sample chamber 320 prior to sampling via purge line 315 and relief valve 316.
When a desired number of samples have been collected, solenoid valve 313 is then opened to allow the collected fluid to be driven from sample chamber 320 to other analysis equipment 330 for analysis. The sampled fluid flows from sample chamber via an exit line 321 and check valve 322.
One or more temperature regulation passages 350 provide heat exchange from the sample chamber 320. Liquid in passage(s) 350 allows stabilization of temperature, and reduces any effect of temperature changes on the composition and viscosity of the sample.
In one embodiment, the sample chamber 320 is a closed end of a piston cylinder. A sample chamber piston 360 allows manual removal of material from sample chamber 320. It also provides for adjustment of sample chamber volume.
In other embodiments, sample chamber 320 may be replaced by any suitable volume for containing the sampled fluid prior to subsequent collection. These alternative volumes may or may not have means for venting or flushing. The sampled fluid (gas and/or liquid) may be collected and analyzed by various means.
Control unit 390 has appropriate hardware and programming for automating the above-described method. It sends control signals to valve 305 to control check valve 303, to valve 309 to control venting of gas, and to valve 318 to control delivery of sample fluid to analysis equipment.
An additional feature of the above-described system is that it resides mainly outside of the engine and has no parts attached to the crank-train. It is capable of taking several micro-samples before sending a larger sample for analysis.
Various methods of sampling fluid from a top land piston crevice may be performed using a bore into which tubing is inserted and using a relief valve and check valve configured as in
