Altitude & Heat: gas/petrol vs. diesel engines

[dieselcruiserhead]

Aftercooling, as a term, actually still is widely used and is the technically correct definitiion. For example all Cummins manuals refer to "intercoolers" as aftercoolers... Air-Air intercooling is something that ideally should be done mathematically correctly (but some of it is a guessing game and this often works fine). If the air-air intercooler and piping is too large, there is noticable turbo lag (time it takes for the power of the turbo to kick in). If it is too small and/or has poor air it is not effective at cooling the air.

They definitely help, but are not necessary IMO. Most diesels these days are turbo charged and intercooled for obvious reasons.

 

[MrBond]

Advice Needed On Small Diesel At High Altitude

Hi There

You guys seem to know what you are talking about so I could really do with some advice on a challenge we have planned for a few weeks time...

We plan to be the first people to take a three wheeled vehicle over the Himalayas.

We will be driving one (actually two) of these: http://www.bajajauto.com/comm_goods_gcmaxd_specs.asp

At the highest peak, we will be 5300 metres high.

The vehicles have 400cc forced air powered diesel engines.

I'm a little concerned that the vehicles just won't work up there. What are your thoughts on this? We are planning on hiring a 4x4 land cruiser as a backup vehicle but not sure even that could tow us out of trouble?


You can find out all about our route on a website I built for the challenge: http://www.rickshaw5000.co.uk/

I'd really appreciate any thoughts on this.

Thanks,

Paul

 

[FellowTraveler]

Consider Hi-pressure Water Injection

RSR racing (motor cycle guys) has the only commercially available high pressure water pump that I know of to properly apply water injection to gas or diesel powered vehicles. Hi-pressure water injection has its roots in aviation to increase power at altitude, when properly applied in a motor vehicle good things start to happen.

Goggle em!

 

[RoyJ]

Just to add a little more detail / confusion into the whole turbocharger thing: a compressor's gas stream output temperature depends on the pressure ratio, not absolute pressure output.

At sea level, if you boost 29.4 psig on a diesel, you have a pressure ratio of 3:1 (atmospheric being 14.7 psia). If you're at high elevation with 13 psi atmospheric, then the same 29.4 psig boost will become 3.4:1. Your compressor output temp will be higher, especially if the compressor was already at the limit (undersized) at sea level. Therefore, the aftercooler is even MORE important at high elevations.

Not only that, because of the lower air density, the same aftercooler / intercooler will not be as effective as it was at sea level, given the same ambient air temp, vehicle speed, and fan rpm.

As to the origional question, a modern NA gas engine will not loose efficiency at high altitudes, just power output. Your hwy cruising mpg will typically rise, because your aero resistance is lower due to thinner air.

 

[rblackwell]

2009/2010 my wife and I drove a 2008 Chevy duramax diesel from the top of North America to the bottom of south america. This is a turbo charged electronically controlled diesel engine. It performed flawlessly.

The highest altitude we reached on this trip was 5000m (thats 16,500ft), see
http://www.whiteacorn.com/theamericas/journals/entries/090913/index.php
and
http://www.whiteacorn.com/theamericas/journals/entries/100529/index.php

We talked to many people with diesel and gas engines about altitude. Turbo'd diesels work well, but for the ones with out electronics (say toyota 70 series, or old Mercedes G-wagons) you need to manually adjust the "mixture" on the fuel pump.

Incidentally we have also started our truck without block heaters in temps as low as -25F

Finally all the tour vehicles in SW bolivia (altitude 14-17,000 ft) are gasoline toyota Landcruisers of Nissan patrols.

Rob

 

[gchinsr]

The main reason turbo engines do better coping with altitude, is the fact they actually produce more boost than required, and extra pressure is released through a waste gate, This over boost ensures the motor has the correct boost pressure to reach the advertised performance. Once the motor starts climbing, it therefore can continue to compensate for the thinning air, until it reaches the limits of the turbo maximum volume and then will start to lose power from that point on. For a vehicle to be used at altitude regularly, it is hard to beat. Water injection is very helpful with turbocharged petrol motors running high boost pressure to reduce detonation. I have also used a water/methanol mix as a means to reduce intake charge temps, which condenses the air into the combustion chamber, gaining a few extra horsepower.
Greg

 

[TreeTopFlyer]

You see a lot of true "intercooling" on yachts with big diesels. They will have both superchargers and turbos, intercoolers and aftercoolers. But these are motors making 1200+HP or more. It's pretty amazing to see all the plumbing.

 

[gchinsr]

It is all about cooling the intake charge in the combustion chamber. The cooler the air, the more dense the the air/fuel mixture will be, making more power. In addition to inter cooling, the new fuel injection systems atomize the fuel directly into the combustion chamber, which has a cooling effect, making them even more efficient. Turbocharging is very efficient, compared to supercharging, which eats power from parasitic losses to drive the compressor. When set ups include both, the supercharger is used first due to instant boost off idle, then once at speed, the exhaust flow spools up the turbo, the turbo will take over with out "lag" for top end power. VW had started using this system on one of the Europe only models a few years back.
Greg

 

[RoyJ]

Greg,

Are you talking about the old Detroit 2 stroke marine motors? Because I have to say, I've never seen a modern 4 stroke diesel with a supercharger and turbocharger.

And for those that don't know, a Detroit needs the "supercharger" to run. Otherwise, it's 2 cycle combustion would have no way of scavenging the exhaust gas. The Eaton roots blower offers no boost what so ever, and is just as starved for oxygen at high altitudes as NA engines. I know because my 6V71 falls flat on its face above 3000'.

 

[gchinsr]

Sorry not being too clear, the twin charged VW is a petrol motor.

 

[bob91yj]

On a two stroke Detroit Diesel the turbo feeds the supercharger.

 

[RoyJ]

Very few 71-series Detroits are turboed, though an 8V-71T can make serious power!

On 92-series, the blower has a bypass. When turbo boost kicks in, they're feeding the engine directly. Again, they have a blower, not supercharger (the Eaton blower makes 0 psi boost)

 

[bob91yj]

Didn't think my answer all the way through before posting, all valid points.