Conclusions and future research directions
Water injection, with an effective cooling effect for the in-cylinder combustion process, has attracted extensive attentions in recent years due to the potential knock mitigation and NO x reduction.
This paper provides a critical review of the current state of the art research on this technique.
After detailed introductions of water injection and evaporation processes, mechanisms of the in-cylinder combustion with water addition were discussed thoroughly.
An in-depth survey of WI applied on different types of ICEs was then conducted followed by the comparisons and combinations of WI with other engine techniques.
Finally, some critical issues were addressed. From the above discussions, the following conclusions are obtained:
(1)
Wall film formation that reduces charge cooling and premature vaporization outside of the cylinder are the main causes for the lower efficiency of the intake runner/port WI implementation, compared to direct or emulsion WI.
An accurate evaluation of the water evaporation shows great importance of the design and optimization of different WI systems, and also for an accurate calculation of the heat release rate.
[I NB that any WI before the airflow meter will result in the metering out of fuel for water vapour gas rather than air...
ie: Any of the clickbait type videos that abound on YouTube should be taken with a pinch of salt]
(2)
For the CI engine, water addition from the “fuel side” has a positive effect on the combustion, while a small negative effect on efficiency is inevitable with the water addition from the surrounding “air side”.
The dilution effect of WI is much larger than the thermal effect and chemical effect on the NOx reduction of the CI engine.
Water directly injected into the combustion zone allows larger decreases of the combustion temperature and therefore the NOx emissions.
This also benefits the NO x and PM trade-off, where NOx reduction is possible without significant impact on PM.
(3)
For the SI engine, water injection mainly slows down the laminar flame speed, but the combustion duration is not significantly affected when combined with an advanced spark timing with a small amount of injected water.
Effects of WI on emissions of SI combustion should be considered with the engine operating conditions and the adjustments of other parameters like the spark timing and AFR.
With the increase of WI amount and the decrease of fuel enrichment, HC and CO decrease simultaneously, but trends are different with WI under stoichiometric operating conditions. Variations of NO x and PM emissions also depend on both the amount of injected water and the in-cylinder air fuel ratio.
(4)
WI has been shown as a cost-effective approach for the downsized gasoline engine operating without fuel enrichment (lambda = 1), and the required water fuel ratio for stoichiometric operation depends on the WI implementation, engine specifications and driving cycles.
Evaluating from an in-cylinder charge cooling point of view, using the same amount of water, direct in-cylinder WI is the best choice, and port WI is better than the upstream WI. Injection pressure, timing and location of water should be optimized with consideration given to the water evaporation, combustion and emissions.
In addition, the selection of WI implementations should be considered with respect to benefits, robustness, packaging and expenditure.
(5)
WI is a good alternative to EGR for introducing inert species into the cylinder, therefore mitigating knock combustion on the SI engine and reducing NO x emissions from the CI engine.
A combination of WI and EGR can further decrease the NO x emissions in the CI engine, and PM emissions (smoke) also decrease compared to the sole EGR solution.
(6)
Combined with a high CR, multistage air charging system or Miller cycle, WI shows great potential on the SI engine for further downsizing, which has been shown to be a cost-effective approach to reduce CO 2 emissions for the new generation of SI engines.
The decreased TIT maybe used as an enabler for employing variable geometry turbines on the gasoline engine, and material costs on the turbocharger can be decreased due to the reduced thermal stress.
It should also be stressed that water injection is still not a mature technique for commercial vehicles. Fundamentals of both thermo-physical and chemical kinetic effects of water addition on combustion phenomena and emissions need to be further investigated with respect to different water injection implementations and engine types.
In addition, only limited amount of studies regarding long term operation using water injection have been published, and
friction analysis on piston ring and engine block, carbon deposit on water injector, metal debris
and water content on lubricating oil and corrosion analysis need to be further evaluated for water injection commercialization.
[I NB that by the addition of Boric Acid to the water all friction concerns are null and void.
In fact the opposite is true and further dramatic improvements in economy, longevity and smoothness will be evident.
But that's a subject for another day.
Anyone interested can start by looking at the research done by Argonne National Labs where it was discovered by Dr Ali Erdemir.
There is a huge amount of subsequent research by other research institutes, as befits such a ground breaking discovery]
Here's a link to a draft of the full paper:
https://purehost.bath.ac.uk/ws/porta...tal/190048010/
NB the BSFC improvement from ~380 g/kWh down to ~230 g/kWh at 2100rpm shown in the graph.
If your ISP has NOT been bribed into flagging Sci-Hub as malicious; you will find a
better formatted version of the paper here:
https://sci-hub.ru/https://www.scien...96890419300883
A search for
engine water injection kits
brings up a great many kits you will now be better equipped to choose from.
There are also a good number of YouTube videos on various makes of kits.
I hope someone finds this useful..?
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