I have never found a good source for describing what the numerous fans on a diesel electric locamotive actually perform. Say, for a example: an SD 40-2 has 2 fans grouped in the middle and 3 grouped toward the end of the long hood for a total of 5. Do some fans suck air into the hood body (and if so to where and why)? Do some air suck air out of the hood body (and if so why?). How about others (like an SD 75)?
Thanks.
On a SD40-2, the two center fans cool the dynamic brake grids while the three towards the rear cool the radiators.
As above, the SD40-2 fans all suck air out of the body, the two over the engine through the dynamic brake resistor grids and the three at the rear through two radiator panels arranged as a vee below the fans.
In the SD40-T2, the SD45-T2 the MP15AC and some other types, the fans are below the radiator and blow air upwards through radiators that are laid flat or nearly so above the fans.
In the SD75, the radiators are larger than those in the SD40-2, but the fans are the same, just further apart. The SD75 dynamic brakes have a single larger fan below the dynamic brake grids which are arranged in a circle (called radial grids) and the fan blows air upward through the grids. This system is MUCH noiser than the older SD40-2 arrangement.
It is worth pointing out that the radiator fans are driven by AC current from the companion alternator, part of (effectively) the generator or main alternator, Thus the fans turn at a speed determined by the speed of the engine and are turned on and off by thermostats on the radiator.
The dynamic brake fans are DC and are powere
Thanks for the great information. I thought perhaps one of the fans sucked air into the engine for combustion. I suppose diesel-electrics just draw it in like in a car or truck? Turbos use exhaust gas back for combustion use, but fresh air gets into the combustion area how? Do the air filters connect to a port directly to the diesel intake manifold? As for the radiator fans, they are serving two purposes: 1) exhaust hot air out above the radiators, and 2) simultaneously draw cooler air thru the outside grills; right?
Thanks again.
I am amazed that nobody has commented on my post…
I should have said that the pressurisation fans, of course sucked air into the body. These were driven by the companion alternator, a D14 I think in the case of the A16C units. The pressurisation fans later received ducts covering them to prevent exhaust gas or dynamic brake outlet air being sucked into the body, since these units ran in the desert and it was pretty hot inside already.
A few hood units of export types G12C, G22C and some G6Bs had pressurisation fans. These all had engine driven radiator fans, and thus had no companion alternator. I hadn’t thought much about what drove the pressurising fan until I saw one removed from a G6B and noticed that it had what looked like a standard air brake hose connected to it… yes, it was driven by compressed air from the locomotive’s main reservoir. That was a lot cheaper than fitting a companion alternator.
The discussion so far has been about EMD fans, because they are visible in a lot of cases, but GE locomotives have unseen radiator fans and dynamic brake fans that deserve some attention.
From the original U25 until the Dash 7 series, the GEs had engine driven radiator fans driven through a right angle gearbox. The U25 had two fans in line fore and aft, but they changed to a single fan from the later U28s onward. EMD actually built one locomotive with the U25 arrangement, two mechanically driven fans in line in the export GT16C for India, which was a sort of export SD24.
GE relied on the radiator fan(s) to cool the dynamic brakes in the U series and earlier Dash 7 series, locating the grids in the air intake below the radiator.
From the Dash 8 series onward GE adopted AC motor driven fans, initially two in line on the earlier units and later a single larger diameter fan under a wider, shorter radiator that projected further beyond the hood on each side. This remained current until the 2014 ES series (although they had two further high speed fans
They draw it in through air filters in an ‘air box’, just as most modern cars or trucks do. In the ‘old days’ many of these filters were oil-bath filters (which were cleaned and re-used), and sometimes had an ‘inertial’ stage (turning the intake air around corners so the larger particulates are separated out, as in a cyclone filter). More modern applications that need better cleaning use replaceable filter elements. I think Mr. Clark knows far more about this than I do, and I welcome his comments in detail both on the historical ‘timeline’ and the evolution of use by specific builders.
I think you may be thinking about two very different things at the same time. Turbochargers use some of the heat in the exhaust gas to run a turbine, which drives a separate compressor that compresses the intake air to higher density. The exhaust from the turbine goes up the stack and is not returned to the engine. The intake air to the compressor, just as in turbocharged cars or trucks, comes through an air filter first.
Exhaust gas recirculation is the use of some of the exhaust to replace air in the intake charge. A specific use of this is to reduce the amount of nitrogen admitted to an engine’s cylinder on the intake stroke, which can cut down the emissions of nitrogen oxides (the NOx that has been so troublesome to CAT and EMD). I don’t know of any use of EGR that circulates the exhaust to a point ahead of the turbocharger, though – it would have to be cooled down to a significant degree to preclude needlessly high post-turbo pressure, or involve a larger (and more expensive) intercooler to take out the extra heat. Again, Mr. Clark will have better detail information on where and how
Firstly, for anyone who didn’t realise, I started my post before VGN Jess reponded and of course didn’t see it until I had posted. I think I may have been distracted in mid post, which didn’t help.
To answer the question about engine inlet air fans, in all of the pressurised export units the engine air was drawn from inside the body, having been drawn in by the fan (which looked just like an EMD 36" radiator fan, incidentally).
One of the innovations introduced by the GE U25 was a sealed carbody with what was called a “centralised air system”, which was copied by both EMD and Alco. This meant that all air went through at least a primary filter, usually an inertial filter and then combustion air went through media filters, usually oil bath originally and later paper. A blower fed the primary air to traction motors. Before this time, locomotives usually had louvres in the hood doors adjacent to the engine air intake with oil bath filters mounted on the inside of the doors. The change occurred with the GP30 with EMD and the “Century Series” for Alco.
The only locomotive type I can recall with a visible inlet air fan is the Alco Century 636 which had a large fan set flush into the top of the intercooler box which fed both the engine and the intercooler radiators just below it (when the external louvres were open). The air then went through primary filters and into a very large main blower, where it went to the traction motors, but also through a duct formed by the main frame beams and sealed off by the fuel tank to the back of the engine and into an “air box” with secondary filters and into the turbocharger, which was on the rear end of an Alco locomotive engine.
One of MLW’s simplifications in the M630 and M636 was to combine the intercooler circuit with the main radiator (which was 1/3 larger than on the M636 compared to the C636). But the combustion air still went under the engine. Some later modifications introduced primary air
Yes, exhaust gas recirculation (EGR) is a process by which some fraction of the exhaust gas is introduced into the intake charge intended to reduce peak combustion temperatures and pressures below which significant amounts of NOx is formed. Peak temperatures are reduced because of the increased heat capacity of the intake charge due to the added mass of the exhaust gases present.
EGR does not reduce the amount of ni
Can you explain this a little better. It doesn’t seem to make full sense to me as written. The “mass” of each of the constituents of recirculated CO2 is very little different from the mass of nitrogen (and at 12 and twice 16 they bracket twice 15), and in any case a mass effect would have little to do with the ‘heat capacity’ of an admitted charge. I don’t have my rubber bible handy, but is the heat capacity of CO2 that much greater than the equivalent number of moles of carbon and oxygen? I suspect you well know what you mean, with CO2 being a denser gas due to its structure, but I’d like to see it worded differently.
My experience with EGR and FGR (the external-combustion analogue) is that just the opposite is true. To the extent CO2 displaces air in the mass of an intake charge, the amount of nitrogen is de facto reduced. To the extent it dissociates at high peak temperatures, it is much more likely to recombine than to preferentially react with a temperature-dissociated N (or allow N to react with available O/O2) to produce NOx. That is recognized as a fundamental element of a number of the ‘cleaner coal’ schemes.
That’s not to take away from the essential point I would make (and I think you are making) – that the major point of EGR is to slow down the oxidative “combustion” reactions taking place after ignition during the power stroke, and thereby decrease the peak temperature achieved during the reaction so that you’ll get adequate expansion due to heat release causing the charge gases to expand (which is what produces the shaft power out of this kind of heat engine) while st
The number that I remember from my engineering thermodynamics class was 2700F - the professor was a member of CARB at the time. He mentioned that a very simple trick to reduce NOx from pre-1971 cars was to retard the spark a few degrees, though at the expense of power and mileage.
A neighbor of one of my high school friends did one science fair project variable EGR, one finding was that a typical car engine from the 1960’s would tolerate a very large amount of EGR at cruising speeds. My recollection was that this was for the 1977 science fair and interestingly enough, he is now a EE prof at Stanford.
Keep in mind that the recirculated exhaust gas has
Remember that this figure is thermal NOx under close to ambient pressure conditions – as in FGR in a power boiler.
This is essentially the principle of the Fish carburetor (and other wonder carburetors) – a very lean, but hot mixture can still ignite (in part via polynucleate autoignition in the cylinder) to produce enough heat/pressure to generate power from an engine. The difficulty is that very small changes in demanded power can (and do) cause an engine operating that way to stall, and a carburetor system has little hope of responding correctly in the timeframe involved. More modern control modalities make this possible … but they are almost always much better employed in injector modulation than in mixture control…
Thank you for reminding me – I got carried away with the pure gases.
By the way, I was wrong. I was disparaging the idea of added nitrogen as a sensible way to decrease NOx. See [url=http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CCcQFjAC&url=http%3A%2F%2Fwww.compactmembrane.com%
After skimming through the article (noting figure 7), it looks like the advantage of the membrane comes more from depletion of oxygen as opposed to enrichment of nitrogen. I’d wonder if more benefit could be achieved by enriching the oxygen content of the supply air and utilizing EGR to keep combustion temperatures under control (or maybe try argon injection…).
One take-away from figure 7 is that the NOx peaks about 35% load with standard air, which suggests the engine is running around 200% theoretical air. Idle is lower as the large amount of excess air quickly cools the combustion products, full power is lower as most of the oxygen is used up by the fuel.
I think you are right; the idea seems to be having an inert-at-prevailing-temp gas in the charge that slows down the oxidative heat release from the fuel without dropping parts of the charge mass below necessary transition temp for the combustion reactions. As I see it, we’re not ‘burning’ the fuel, we’re converting it to power gas as nearly at stoich as possible, and the nitrogen serves as a diluent to keep peak reaction temperature below critical.
A problem with argon injection is that you’d have to carry a pressure bottle of argon with you… or have a really, REALLY fancy arrangement to get 1/120 or so of the atmosphere separated out in realtime. The CO2 in EGR does this job every bit as well as a noble gas (remember what a good shielding gas it can be) and is not only free but serves a noble purpose (I couldn’t resist the pun) in adaptive re-use. One point they stress in the nitrogen-enrichment application is that very little equipment is required to obtain the relatively slight enrichment of N2 they’re using, and the supply of N2 is essentially limitless with no ‘user service’ being required (and of course no SCR rigmarole added on top of the EGR system).
My approach has always favored, as you say, enriching the oxygen content in the charge (so you need a lower charge mass of ‘air’ including a proportion of nitrogen, and then trying to run the charge as hot as possible to keep the thermodynamic efficiency up. Note that this usually involves higher peak cylinder pressure, for which the
Wizlish (and all others): Thank you for all the information. I felt my questions were initially “dumb”, but in reading the responses to date, I understand all the EMD hood type fans are interesting to others as well and I’m glad I asked. I have a 100% better understanding now. I am a big TrainSimulator 2015 user and often wondered about the fans used on the EMD locomotives in that application, such as: GP7s, GP9s, FA7s, GP38-2s, SD 40-2s, SD45s, SD60s, SD70s, sD70ACes, and SD80MACs. Thanks again!!!
The next thing you might want to ask is why some of the fans have irregular blade spacing… and how the blades are shaped and flow-streamlined to minimize noise. Ask M636 about Q-fans, for instance.
I’ve always had a number of questions about EMD fans. Might as well ask here I guess. 1: if the standard Radiator configuration on EMD was causing issues in tunnels such that SP and Rio Grande got Tunnel motors…which mimic designs from EMD competitors, Why did EMD go back to their classic design with the 50/60/70 series? Why not simply switch to all T motors all the time? And how is it that SP and DRGW and Now UP don’t have the same problems with their SD50s/60s/70s in the Tunnels? 2: 2 Ex-SP SD40T-2s are currently in Tacoma (SusieQ units) rumor has it they are getting ECO upgrades. My question is this. I assume that the V8 2150HP ECO would require no Radiator mods to work, but does the radiator in general have the same cooling capacity as a standard SD40-2?
Firstly to deal with YoHo’s point about “Q-Fans”.
There is a classic line about “wasted youth” in Pool Halls, but I have wasted much of my late middle age and early old age on a footbridge in Moss Vale where good photos can be taken in the early afternoon of north bound freight trains. However, locomotive for local limestone shuttle trains literally refuel under the bridge so I’ve seen a number of EMD fans (on JT26C-2SS) stopped literally a couple of inches below my feet (the bridge built in 1915 is right on the clearance limit).
The fans appear to be designed (from memory) with sixteen fan blade positions of which twelve are filled with four evenly spaced gaps. Even with gaps the fans need to be accurately balanced, of course.
What is the advantage of unevenly spaced blades? The blade passing frequency if constant, would excite a resonance which would form a major part of fan noise. By leaving every fourth blade out, the resonance does not build up and that source of noise is eliminated or substantially reduced.
I’m not familiar with the other airflow details of Q Fans. I did see a description years ago…
I understand the “tunnel” radiator arrangement was requested by Southern Pacific because of overheating in tunnels and snow sheds, particularly with the SD 45. The GE U36C and similar units did not suffer this problem, at least partly due to drawing the air from frame level where it was cooler and not mixed with radiator outlet air and exhaust.
By placing the fans under the radiator, the air velocity through the radiator is increased. This allows the radiator to regain normal temperature more quickly (between tunnels). The down side is that the air drawn from nearer the track has more dust and grit and the higher air velocity erodes the copper of radiator cores more quickly so the radiator doesn’t last as long.
So there are swings and roundabouts…
EMD decided that their original layout was