Internal combustion engines for Mars

tahanson43206 · 2022-04-30 04:17:19

For kbd512 re Cummins Diesel suggestion in Post #225

Thank you for suggesting a specific engine that might be upgraded for Mars service.

It appears that on Earth, this model can provide in excess of 180 horsepower, using diesel fuel and oxygen mediated by 80% nitrogen.

Because CO has so much less energy per unit of volume, I'd expect performance to be less on Mars, so would appreciate a clarification on that point.

You've introduced the possibility that the thin Mars atmosphere might be able to cool this engine, but there ** is ** another alternative...

If both the fuel and oxidizer are carried in liquid form, then the engine could be cooled by pre-heating those.

I'll assume for the moment the scenario you've outlined is possible, in the Real Universe.

Next post ...

(th)

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(th)

tahanson43206 · 2022-04-30 04:18:10

For kbd512 re Cummins Diesel suggestion in Post #225

Assuming the engine (or one like it) would work on Mars with CO as fuel, and Oxygen tempered by CO2 filler as oxidizer, the next subtopic that might flow from this one is machine options...

Any machine designed for Mars, using this engine or one like it, would be encumbered by the need to carry large fuel and oxidizer tanks, in order for it to offer any useful work life.

Power delivery options would include:

1) Direct mechanical (eg, wheels/tracks for mobility)
2) Hydraulic for manipulator arms of various kinds
3) Electric (for computer controls as a primary "customer"), and potentially for electric manipulators.

A wide variety of machine types ** should ** flow from this point.

All ** should ** be teleoperated ... there is no need to design any machine for Mars that needs a human being in the cab, except to drive it back to the shop if the teleoperation systems fail.

(th)

tahanson43206 · 2022-04-30 04:43:51

For All...

Last year, GW Johnson prepared a proposal for a "Real Universe" drill to be deployed on Mars to investigate two things:

1) Presence of water well below the surface (eg, 10 meters)
2) Quality of surface for a prospective landing site

The target date for launch was September of 2022, and that was always an ambitious target date.

The proposal was sent to two primary recipients, and copies were sent to key players in the space development community.

No response has arrived from anyone. That is not surprising to me. It is standard practice in (US) industry to NOT acknowledge unsolicited suggestions.

It would have been different (I am confident) if GW had the backing of a ** very large ** funder, so that the risks of a venture along these lines would be less for the service provider.

In recent posts, kbd512 has floated the name of Cummins Diesel as the potential supplier of an internal combustion engine for the Mars market.

It is not yet clear (to me for sure) the engine suggestion can survive the brutal examination it is about to receive.

However, that is not the part of this operation I'll be helping to advance. What I can do is to offer encouragement to our members to look for opportunities to win a substantial part of the machine business for Mars development.

This forum has spent a lot of time, and invested a lot of thought and emotional energy thinking about early exploration and the challenges of first flights.

My interest is in the robust development that needs to follow, to support the large population that is likely on Mars, in coming decades.

(th)

GW Johnson · 2022-04-30 08:50:58

Internal combustion engines on Mars require you not only to store the fuel in a tank, but also the oxidant. You cannot get the combustion energy out of the fuel unless you have both fuel AND OXIDANT available at suitable inlet conditions for the engine. That would be in the range of 0.5 to 1 atm pressure at the intake suction point, because that is where ALL of our collective experience with internal combustion engines lies.

Those two things being true, has two very important consequences for adapting this technology to use it on Mars.

First, you WILL NOT BE COMPRESSING the Martian atmosphere real-time for either its use as a diluent for your oxygen, or as the oxidant for some sort of fuel that burns with Martian CO2 (magnesium is such a fuel). Compressing 6-7 mbar to 500-1000 mbar is a compression ratio in the 70:1 to 167:1 range. That looks like a vacuum pump, more than any sort of compressor ever devised by humans. Such vacuum pumps are big heavy pieces of machinery, with a big power draw and very little throughput massflow. Such are not at all suitable for real time use doing anything. Which in turn means if you use the CO2 as a diluent gas, you have to store it in a third tank and deliver it to the engine inlet at that same 0.5 to 1 atm pressure, real-time.

Second, since you have to carry your oxidant and supply it to the engine inlet at 0.5-1 atm real-time, meaning you must put it in a suitable tank alongside your fuel, you CANNOT GET THE FUEL ENERGY OUT without having BOTH reactants suitably stored. Therefore, the stored energy density of your system must be the energy release divided by the sum of BOTH stored reactant masses!

The ONLY reason we get away with customarily using energy release per unit mass of only-the-fuel here on Earth, is that the oxidant is all around you, already at a suitable pressure, and you don't have to store it aboard. What we are really talking about is energy release per unit mass of stored reactants, and on Earth we only have to store the fuel. That simply IS NOT TRUE on Mars!

An empirical formula for a generic hydrocarbon fuel would be CH2. To oxidize it at more-or-less stoichiometric conditions inside a piston engine, the balance resembles 1.0 CH2 + 1.5 O2 = 1.0 CO2 + 1.0 H20, for which the oxygen/fuel ratio by mass is 1.5*32/1*14 = 3.43. What that means on Earth is about 19,000 BTU release per each pound of stored fuel, for a storage energy storage density of 19,000 BTU/lb. What that means on Mars is that the energy storage density is 19,000 BTU per 4.43 pounds of reactants we must suitably store, or a storage energy density of only 4290 BTU/lb. You not only have to store the 1 pound of fuel, YOU ALSO HAVE TO STORE the 3.43 pounds of oxygen! There are 4.43 pounds of reactants to store on Mars, and they only release that same 19,000 BTU.

Assuming we can redesign the piston engine to handle hotter flame temperatures by about 1000 F (no mean feat in and of itself), then a hydrocarbon fuel burned with stored oxygen on Mars is one means of energy storage for transport or shaft power. If you cannot handle the heat, then you add a third stored "reactant", the diluent gas, which further dilutes the storage energy density. Myself, I'd rather just redesign to handle the hotter gases. But that is NOT a trivial exercise!

Here is why I would avoid the dilution approach: assume we need the compressed CO2 as diluent gas, in the same mass ratio as the nitrogen and oxygen here on Earth in our air. That would be 3.31 lb of CO2 for each 1 lb of O2. The 1 lb of fuel requires 3.43 lb of oxygen, requiring in turn 3.43 * 3.31 = 11.35 lb of diluent CO2. Now, your stored reactants total 1 + 3.43 + 11.35 = 15.78 lb, and you STILL only release 19,000 BTU from the reaction. That's now a storage energy release density of 19,000/15.78 = 1204 BTU/lb.

Excuse me for working in the US customary units that I am more comfortable with. Here are the conversions:

19,000 BTU/lb *1055 W-s/BTU * 2.205 lb/kg /3600 s/hr = 19,000 BTU/lb * .6462 W-hr/kg per BTU/lb = 12,280 W-hr /kg = 12.28 KW-hr/kg. That's the energy storage density for using a hydrocarbon fuel here on Earth.

On Mars without dilution, it is 4290 * .6462 = 2772 W-hr/kg (of stored fuel + stored oxygen) = 2.772 KW-hr/kg. That's better than a battery, but not very dramatically so, not like here on Earth were oxygen-bearing air at suitable pressure is free all around you.

Using stored CO2 dilution at the Earthly ratio, it is 1204 * .6462 = 778.0 W-hr/kg = 0.7780 KW-hr/kg (of stored fuel + stored oxygen + stored diluent). That last is no better than current lithium-ion batteries, maybe not quite as good.

What's confusing the issue about this is that with a battery, there is ONLY the mass of the battery in which you store releasable energy. The energy stored divided by the battery mass IS the storage energy density. You have to do it EXACTLY the same way for a fair comparison with combustion engines burning fuel: releasable energy divided by the mass of the stored reactants required to release that energy.

Here on Earth, we need ONLY store the fuel. The air is free all around you, and at a suitable pressure for the engine inlet. You need not store it. That is why the storage energy density for hydrocarbon fuels is the 19,000 BTU from each lb of stored fuel ONLY!

You have no air bearing oxygen at a suitable pressure on Mars (or the moon, or anywhere else off Earth). You have to divide the releasable energy from your chemical reaction by the sum of ALL the reactants you have to store! Otherwise, the storage energy density comparison is not fair.

You will SERIOUSLY mislead yourself if you just use the traditional Earthly fuel heating value off of Earth!

And I have not yet addressed the cooling radiator at all! Those are not really "radiators", they are convection devices. At 6-7 mbar, it will be very hard to get the cooling "air" massflow out of the fan, and the heat transfer coefficients for the tube fins will be more than an order of magnitude smaller than we are used to. Most of the 19,000 BTU released must be disposed-of as waste heat, because the energy conversion efficiency of most piston engines falls in the 10-25% range at full load, and 0% at idle.

GW

Last edited by GW Johnson (2022-04-30 10:41:12)

tahanson43206 · 2022-04-30 09:33:37

For GW Johnson re Post #229

The following quote caught my eye ...

Second, since you have to carry your oxidant and supply it to the engine inlet at 0.5-1 atm real-time, meaning you must put it in a suitable tank alongside your fuel, you CANNOT GET THE FUEL EBERGY OUT with having both reactants suitably stored. Therefore, the stored energy density must be the energy release divided by the sum of both stored reactant masses. The ONLY reason we get away with energy release per unit mass of only-the-fuel here on Earth, is that the oxidant is all around you, already at a suitable pressure, and you don't have to store it aboard.

If you have a bit of spare time, please clarify a point ...

The energy released by a chemical reaction does not depend upon how it is stored.

The quote above seems to imply the energy released id reduced because the oxidizer is carried on the vehicle.

I suspect i just don't understand the wording.

The energy released in a rocket engine does not decrease because the fuel and oxygen are carried on the vehicle in separate tanks.

Thanks for that clarification.

(th)

tahanson43206 · 2022-04-30 09:38:27

For all contributing to this topic ...

In post #229, GW Johnson brings up an important point that I would appreciate someone(s) discussing...

The issue at hand is (a) the need for diluent to protect the machinery by absorbing some of the thermal energy, and (b) the need to carry the diluent in a separate tank.

Question #1: can the diluent and the oxidizer be carried in the same tank. premixed to optimum density?

Question #2: Per kbd512, CO may be difficult to ignite.

If CO is sufficiently difficult to ignite, can it be premixed as a monopropellant like hydrazine?

In other words, can we achieve an optimum mixture to be fed into the engine with just one tank?

Does this permit elimination of some components of the engine related to mixing of fuel and oxidizer?

(th)

tahanson43206 · 2022-04-30 09:43:11

Special for kbd512 ....

In an earlier post, you provided a suggestion for an (almost) stock engine that could (with modification) serve on Mars with CO as fuel and O2 as oxidizer.

You had suggested CO2 might act as a diluent, and GW Johnson has added support to that idea.

Given the idea/suggestion of combining oxygen and CO2 in a single tank, premixed to optimum ratio for the best performance of the engine AND for the optimum temperatures to be created, by any chance, can you estimate the optimum ratio of CO2 to O2 in the tank?

(th)

GW Johnson · 2022-04-30 10:21:44

I finished post 229. Go back and look at it again. In particular, look at what happens to storage energy density when you use dilution, instead of redesigning for higher flame temperatures.

Yes, internal combustion engines could be used on Mars. No, they will not be in near-stock form, unless you do dilution to cool the pure oxygen flame. And if you do, the energy storage density is no better than a battery.

GW

Last edited by GW Johnson (2022-04-30 10:25:13)

SpaceNut · 2022-04-30 10:36:35

The engine starts in a cold environment so any coolant must not have freeze expansion for the radiator portion of the system of which water would have for an issue.
The lubricant is more internal which means the sleeve between the cooling and cylinder walls are thicker as a mass absorbing system and the internal wall that separates the oils from the coolant as well. We could also air cool the oil as well as to give as secondary coolant as well to moderate the internal temperatures of the engine.
Its one of the reasons for starting with a diesel engine rather than a gas engine as the walls are already thicker.

kbd512 · 2022-04-30 11:37:16

tahanson43206,

We need to cool the engine using a traditional radiator and fan setup. The fan must be rather large and spin just below the speed of sound (same rpm as the Mars helicopter blades). Radiator will be a large but thin single-row pure Copper design with a graphene-based electrophoretic coating to assist with thermal power transfer.

We will obtain the required performance level by injecting more fuel / oxidizer, which is the only way you make more power with a given engine design, as well as using a much better buffer gas than Nitrogen, namely CO2, which is quite famous for its ability to re-radiate heat and it has a much-needed density improvement when compared to Nitrogen.

If the engine rotates at 2,500rpm, then you need 5752.5L of CO2 per hour (if CO2 had the same density as Nitrogen)

5.9L displacement * (2,500rpm/2 (four-stroke)) = 7,375L of air (air is 78% Nitrogen / diluent gas)
7,375L * 0.78 = 5,752.5L of diluent gas

At 0°C and 1ATM, 1,000L of CO2 gas is 1.977kg.
LCO2 at 20°C and 56ATM is 0.77kg/L, so 2.567.5L.
To store 5,752.5L of LCO2 diluent gas, we need 14.77L of volume, which is about 3.9 gallons.
N2 is 1.1606kg/L

There are 2 reasons it will be less than 3.9 gallons though:
1. We're recirculating lots of exhaust gas to keep the engine hot enough
2. CO2 is much heavier than Nitrogen. N2 is 1.25g/L, CO2 is 1.977g/L (CO2 is about 58% heavier than N2, which should mean you need to use less CO2 as a compressible working fluid)

2021 Toyota Mirai's 10,000psi CFRP tanks are 60L in volume, weigh 24kg each, and can store 46.2kg of LCO2. 3 tanks will be used to store O2 (oxidizer), CO (fuel), and CO2 (diluent gas / working fluid). A 60L Mirai tank therefore stores about 4.06 hours of diluent CO2 gas at full rated engine output, ignoring the fact that CO2 is 58% heavier than N2, so it actually stores 6.42 hours of diluent CO2 gas. Since the tank is rated to handle 10X more pressure than we're throwing at it, we can increase the fluid's bulk density using more pressure.

The 2021 Mirai's fuel cell technology has also been shrunk to 56kg in weight, 37L in volume, and output is 114kWe / 154hp (3.1kWe/L), but it also uses a 13L voltage boost converter and I have no idea what that component weighs. All other components weigh 172kg. A Cummins 6BT, Earth-bound variety, is about 545kg ready-to-run. Mirai's full refueling time has also been reduced to 3 minutes, which is as good as gasoline or diesel. Apart from its pair of 60L H2 tanks, everything else has been shrunk to the point that it fits under the floor of the Mirai cross-over. This is pertinent because power output is 153hp at a weight and volume drastically less than a O2/CO/CO2-fueled Cummins 6BT. I estimate Mirai's system is about 1/3rd the weight, or less, when compared to the Cummins setup. However, Mirai's fuel cell and battery setup does have a byzantine amount of electronic control required- it's spaceship-type technology. Worse still, it requires pure H2 gas at extreme pressure and would still require an O2 tank on Mars. That said, Mirai has decreased total weight and volume by 50% from 2008 to 2021. All existing batteries have not done nearly as well. Give Toyota's engineers another 10 years and they'll have a 150hp to 180hp fuel cell that fits entirely within the engine bay of an existing car.

Toyota - Outline of the Mirai

Anyway...

O2 is 1.428g/L at STP. 10,000psi is 680.272ATM, so O2 at 10,000psi and room temperature is 971.429g/L, so a 60L tank can store 58,285.714g or 58.286kg.

CO is 1.25g/L at STP. 10,000psi is 680.272ATM, so CO at 10,000psi and room temperature is 850.340g/L, so a 60L tank can store 51,020.408g or 51.02kg.

The molar mass of CO is about 28 and the molar mass of O2 is about 32, so we need a little over 2 tanks of CO for every tank of O2 that we plan on using, since 2CO + O2 = 2CO2.

This is clearly going to be heavy, but not dramatically heavier than a traditional Earth-bound diesel engine. It's certainly lighter than a battery pack providing equivalent power output. This powerplant is for a piece of heavy construction equipment that requires a big chunk of metal to act as a counterweight, so it may as well come in the form of a great big engine and fuel mass instead of stacks of metal plates.

kbd512 · 2022-04-30 11:51:01

GW,

Modern batteries require cooling systems, operate over very narrow temperature ranges, and require highly sophisticated control electronics boxes and power inverters. That's apples-to-apples. You can consider the electric motor and the power cables to the motors to be part of the overall drivetrain, just as bell housings / transmissions / drive sprockets / axles / gearboxes may be considered part of the drivetrain mass for a traditional combustion engine powered vehicle, but the battery plus battery cooling system plus power inverter is what delivers usable power to an electronic vehicle's drivetrain.

Remove the cooling system from a Tesla's battery pack and see if that great big battery lasts for more than 10 minutes. I can guarantee you that it won't, which is why Tesla put it there. Remove the power inverter and see if those electric motors still function. Again, you already know what will happen.

There's not one electric vehicle that's even comparable in weight to its gasoline powered equivalent. A battery can deliver a surge of power and that's what makes them fun to drive, but I can crank up the boost and make a lot more power for a lot less weight than any kind of battery.

tahanson43206 · 2022-04-30 13:20:18

For SpaceNut re #234

SpaceNut wrote:

The engine starts in a cold environment so any coolant must not have freeze expansion for the radiator portion of the system of which water would have for an issue.
The lubricant is more internal which means the sleeve between the cooling and cylinder walls are thicker as a mass absorbing system and the internal wall that separates the oils from the coolant as well. We could also air cool the oil as well as to give as secondary coolant as well to moderate the internal temperatures of the engine.
Its one of the reasons for starting with a diesel engine rather than a gas engine as the walls are already thicker.

Thanks for continuing to work on the coolant part of the design problem.

There are two ways (that I am aware of) to approach this ...

The first is operational ... you would instruct your customer to keep the temperature of the machine above the freezing point of the coolant you provide.

If the machine cannot be kept above the required temperature (for example during shipment to Mars) you would instruct your customer to drain the cooling lines and cavities, and (perhaps) to flush the system with a gas until moisture is not detected in the exhaust.

The second is design of the coolant ...

Humans have been operating complex internal combustion engines on Earth in severe cold conditions since at least the days of the Arctic and antArctic explorers. By now, I expect we (humans) have a decent grasp of what is required to provide a coolant for a machine that will operate on Mars (assuming the operator follows your instruction for care and maintenance).

If you are willing, please report what coolant(s) you would recommend for this application.

(th)

tahanson43206 · 2022-04-30 13:26:15

To all contributing to this topic ...

I have proposed that CO2 and oxygen be combined in a fluid that would be stored in a single tank on board a Mars machine powered with an IC engine.

There is NO need for the two gases to be stored separately.

I have asked if all three gases can be combined, since kbd512 has indicated that CO is difficult to ignite.

If all three gases can be combined in a single fluid, mixed in exactly the proportions needed for service on Mars, then we need only one tank, or if we have multiple tanks they will all contain the same liquid.

***
For kbd512

A rocket engine does NOT using cooling fins to keep cool.

Instead, ** every ** liquid fueled rocket engine that I know about (admittedly not all or even a significant fraction) uses cooling by the cryogenic liquids stored in the tanks above the engine.

I expect that a machine designed for the Mars environment could employ exactly the same cooling method.

Elimination of the fragile radiator would simplify the design, if it is in fact feasible to follow the example of rocket designs.

(th)

kbd512 · 2022-04-30 16:14:58

tahanson43206,

The short answer is "no". The detailed answer is, "Why would we invent new ways to kill people?" Every type of gas storage tank should have a different diameter fill fitting to prevent people from filling Oxygen tanks with Carbon Monoxide or doing something similarly dangerous and potentially fatal. Generally speaking, combining your fuel with your oxidizer is a very bad idea for any number of reasons. ANFO is great for mining operations because it's combined into an explosive mixture onsite and the components are stored separately where they pose less of a hazard to the workers using it for blasting. The same concept is at play here. Storing multiple types of gases within the same container also complicates material compatibility. We definitely don't want material degradation issues with the tanks or any part of the fuel delivery system.

We want dozens of hand-transportable gas tanks that are used for specific purposes. We do not want gigantic tanks of mixed oxidizer / fuel / diluent gas that will never be used for any other purpose or dismounted from vehicles without the use of cranes. If a piece of construction equipment will no longer be used or is used infrequently, then we want to easily strip parts from that vehicle to supply other working vehicles currently in-use. Securing much smaller tanks to vehicles is also easier to do. There's a weight penalty, but it's relatively minor.

O2 is a dual-use oxidizer / breathing gas. O2 tanks can be used with any kind of fuel and to produce energy for machinery or to keep people alive. Contaminating them with other gases is not what we want. CO is a dual-use fuel / industrial chemical that can also be used to make hydrocarbon fuels. LCO2 is a dual-use diluent gas / industrial chemical / CO2 source for "air" powered tools. CO2 is also a precursor chemical to hydrocarbon fuels. We need to keep them separated so that whatever supply of gases is available, they can be readily used for whatever purposes after we expend the energy to separate and store those gases.

The advantage to CO/O2 is less embodied energy in the fuel and we would dump pure CO2 overboard rather than try to recover it. If one of the combustion byproducts is H2O, since water is very hard to come by on Mars, we would want to try to recover that. We partially offset that disadvantage by running the engine hotter.

The primary advantage to using an all-mechanical combustion engine is that when it wears out, you do some minor machining and then you can reuse most of the engine. Since it requires no electronics to run, it doesn't really matter what kind of radiation environment it's subjected to, at least over the span of a human lifetime. On Mars, said engine will not rust or corrode, because there's not enough O2 or H2O for that to happen.

A Cummins 6BT all-mechanical variant is a million mile engine at standard rated output. After a million miles, you tear it down, clean it, replace bearings and seals as required, and then you put it back together again. Generally accepted practice is to do that about 3 to 4 times before the block, head, and crank are considered "junk" and need to be replaced. When a Lithium-ion battery wears out, it has to be completely remanufactured, meaning broken down into its constituent elements and totally rebuilt into a brand new battery. No battery of practical weight will last for 4 million miles, and it loses capacity with every successive charge / discharge cycle. It also loses capacity if you don't use it. The 6BT doesn't work the same way. As long as you change the oil and keep the fuel source clean, it will continue to perform, almost as well as it did when new. Given the quality of parts we're using, a 6BT can last the better part of a human lifetime. There are diesel engines from the 70s and 80s that are still in-use today, in their original roles as heavy duty engines for trucks and farming equipment. There are no batteries from the 70s or 80s that are still in-use. 20 years from now none of the Lithium-ion batteries presently in-use, will still be in-use, in any capacity.

If we pay the colossal amount of money required to ship anything to Mars, then we want it to literally last a human lifetime. We don't want throw-away appliances. That lesson has not been learned here on Earth, either. It took a truck load of energy to make a vehicle of any description, so the best thing you could possibly do for the environment is to build it once and build it to last for a human lifetime. The longer a given tool or appliance or durable good lasts, the less environmental impact manufacturing it had.

SpaceNut · 2022-04-30 17:57:46

The fact that we use drops of fuel would also mean that we would be doing the same for mars fuels. The issue is getting pressure for the co2 to be able to have enough for that drop to make it happen. Usually its the heads that fracture due to temperature increase and not the block unless its to cold. The head valve area to exhaust is where its usually the thinnest for the metal for where the cracks will occur.

I would suspect that the water in the atmosphere we would want to drain off in the fuel storage tanks. So there really should not be much water in the exhaust.

Th yes we use the fuel to cool the engine of a rocket but that is a chamber made by the nozzle and it makes nothing moves as does the ICE.

Radiator for mars would be more like tubing sort of like the back of the refrigerators heat exchange grid for air to pass through something like this.

I agree kbd512 that the spark control needs to be simple and not computer controlled so as to make it repairable for sure.

kbd512 · 2022-04-30 19:07:02

SpaceNut,

We seem to need a high-temperature battery that helps bring the engine up to temperature before starting is attempted. Sodium-Nickel-Chloride batteries immediately come to mind. They like heat and lots of it, typically operating somewhere between 270°C and 350°C, so they will both survive and thrive in a high-heat engine compartment. So long as they are well-insulated and are kept warm during operation by exhaust gases from the engine, they will both warm and start the engine the next morning following a mildly cryogenic Martian night. The vehicle may need to be kept "plugged in" overnight without high temperature batteries. If that is undesirable, then a RTG could supply the thermal power to keep the engine warm. However, that would also increase cost and we're already talking about a very expensive engine.

In keeping with the theme of an all-mechanical engine with no electronics or electrical parts, what about a non-battery and non-nuclear solution such as a CO/O2 burner that preheats the engine block?

There are ways to light that off by hand.

If you had a wind-up or air-start device, since you already require onboard CO and O2 gases, then that would provide plenty of starting power. An air-starter could be fairly lightweight, relative to wind-up or electric motor type starters, and very reliable (no more moving parts than an electric motor, no springs, no electricity required). A pyrotechnic starter is another option, but I think wind-up or air-start is sufficient.

Caterpillar 3508 - Big 35 Liter V8 Diesel Engines with Air Starter

Edit: All starters contain at least one spring, but the wind-up / spring-starters contain a series of very highly loaded springs, which is what provides the force to start the engine.

Last edited by kbd512 (2022-04-30 19:18:08)

SpaceNut · 2022-04-30 20:09:01

We know from the rovers that a battery needs a minimum level of power to keep it warm throughout a mars night even when its protected.

Since this could be mobile and fixed the use of how we start and control its operating temperatures are different.

For a mobile unit we could do the inductive RF coil ac power coupling to the warming system if its parked in a particular spot each night.

Plus if we are using it by man we can plug it in each night otherwise plan for tele-robotic use.

That said the battery then becomes a non issue and works as you documented.

kbd512 · 2022-04-30 21:14:28

SpaceNut,

RF inductive coil to heat up an engine block? Where is the power for that coming from? Burn some of the fuel and oxidizer to heat up the block and call it a day. I know that's very unsophisticated, but that's what makes it a good solution. Why invent new problems to solve?

tahanson43206 · 2022-05-01 06:18:48

For kbd512 and SpaceNut ....

Thanks for an interesting exchange about practical issues! We (humans) have been dealing with cold blocks for over 100 years now. If anyone has time to do a bit of research, I'd be interested to know what's been done.

I'll toss in the electric dipstick heater that I've read about. The power for that came from the utility lines.

However, I'm wondering about engines in the Arctic and the Antarctic.

There's a cable TV show about Buffalo Airlines in the far North of Canada. I vaguely recall external machines used to warm the engines before an attempt is made to start them.

For kbd512 ... I like your idea in general, but am wondering how it would work in practice?

Has anyone on Earth ever tried the remedy you've proposed? It seems so sensible, it must have been used.

For SpaceNut ... RF does seem a bit over-the-top.... how about a simple dip-stick heater?

kbd512 wants to know where the power is coming from, and I think that is a fair question.

Thanks to everyone for keeping the momentum going here!

I ** think ** there's some progress happening, although we don't have a proposal to take to the funders yet.

(th)

kbd512 · 2022-05-01 11:05:30

tahanson43206,

Universal Engine Heater Company - Propane Engine Block Heater

From their web page:

We have been manufacturing our propane engine block heaters since 1950.
That is over 68 years on the market!

O2, H2, CO, CH4, C3H8 all remain in their gas phase at the temperatures encountered on Mars, and will never freeze.

Do you old timers remember the world that came before electronic everything?

That world required more periodic maintenance, but it was maintenance that could be done with hand tools and did not require a computer to tell you what was wrong with the engine. It was highly reliable in its own way, which was and still is useful when you are betting your life on your technology working, and obviously less subject to the degradation that all electronics are subject to.

tahanson43206 · 2022-05-01 12:31:50

For kbd512 re #245

Thanks for the clarification in this post ... I now understand how we diverged with regard to cooling ...

I was assuming that the fuel and oxidizer and diluent would all be liquefied.

If the inputs are all liquefied, then they should be able to keep the engine block cool enough to prevent melting.

However, if the liquids are under pressure, as your scenario proposes, then the cooling effect of releasing pressure from the tank is much less.

It should be possible (I can't do it, but I've seen others) to compute the heat absorbing capacity of liquefied inputs compared to gaseous state inputs, and determine the probability of successful cooling of an engine operating at full power for some period of time.

The length of time the engine can operate will depend (of course) on the amount of input available, and the rate of consumption chosen.

If the task at hand is to drive a bore head for a tunnel, it ** should ** be possible to derive the quantities of input needed to achieve the desired performance for some period of time.

That period of time, whatever it is, will determine how long the machine can remain at the bore head before it has to be pulled back for maintenance/refueling.

I'd like to see a design flow from this topic that does not require non-stock components.

If the machine appears to require non-stock components, then (I'm hoping) a way of operating that does ** not ** require anything out of the ordinary can be found.

Earlier, the idea of burning CO with O2 led to realization the temperatures involved would melt a standard engine.

It was proposed that CO2 be added to the input to absorb some of the thermal energy, and (i presume) to contribute to the transfer of thermal energy to mechanical motion of the piston.

It was proposed that a radiator be fashioned with a fan that operates as fast as a Mars helicopter blade.

That suggestion seems overly risky to me, so I am offering liquefied inputs as an alternative.

I've pointed out that many rocket engines avoid melting by circulating liquid (cryogenic) fluids where heat needs to be removed.

I see no reason at all why that technique would not work for an internal combustion engine.

I saw an argument a few posts back, that a rocket engine is different from an internal combustion engine, because a rocket engine has no moving parts. While that is true, the movement of the parts does not seem (to me at least) to have anything to do with the need to remove heat.

An internal combustion engine can remove heat by sending coolant through a radiator exposed to Mars air, or it can send coolant through a radiator cooled by cryogenic liquids.

As far as the engine block is concerned, the coolant comes back ready to pick up another load of thermal energy.

(th)

tahanson43206 · 2022-05-01 13:04:56

Glowplugs is / are the focus of this post ...

The diesel fuel is not the only thing heated by the glow plugs. It also aids in the heating of the entire engine to ensure appropriate operation from the start.

https://www.engineerine.com/2022/01/how … ngine.html

The article at the web site above also reports that glow plugs are a permanent fixture of some model engines.

I bring this up because a glow plug might work for CO/O2 ignition.

It has been reported (earlier in this topic) that an oversized or extra vigorous spark ignition may be required if CO is the fuel.

I am looking for an engine concept that will run on CO without extensive modification for Mars.

We (forum) don't seem to be "there yet".

(th)

kbd512 · 2022-05-01 15:43:21

tahanson43206,

The CO2 diluent gas primarily absorbs the thermal energy released from CO/O2 combustion and expands. In addition to serving as the working fluid for the combustible mixture to act upon, the CO2 "intake charge" helps to keep combustion temperatures within tolerable limits for the engine. The CO2 is used as an inert expansion gas replacement for N2, which is not plentiful on Mars. The heat of combustion expands CO2 instead of N2 inside the combustion chamber. Less CO2 is required in practice because CO2 (44g/mol) is a heavier molecule than N2 (28g/mol), about 57% heavier. At a prototypical combustion temperature inside a normal diesel engine at the moment the mixture lights off, 3,860°F / 2400K, specific heat of CO2 is 1.393 and specific heat of N2 is 1.304, so 89J of additional energy had to be added to CO2 to raise its temperature by 1 additional degree. Since the mass of compressible gas / fluid pressing down on the piston with great force / pressure is what produces our engine power output, then we need considerably less CO2 than N2. Requiring 57% less volume of "intake charge", for equivalent weight as N2, to compress and expand is pretty significant since it means less volume of CO2 can be expanded to perform the same amount of work. We do need more oxidizer and fuel, about 7% to 10% more in rough terms, to provide an equivalent temperature rise and attendant pressure increase inside the combustion chamber, relative to what would be required if N2 was our primary working fluid. Since the mass of expanding combustion products and inert gas is higher in CO / O2 combustion (all CO2, no H2O or NOx), the end result may be a wash or it may slightly favor CO / O2 (but I haven't done the math on this). I can tell you that CO / O2 combustion produces significantly less heat than CH4 / O2 combustion, so you will definitely need more CO to combust. CO is 10,104kJ/kg. CH4 is 55,514kJ/kg.

That's a fairly steep embodied energy imbalance to overcome, but maybe not if the following process can be scaled up:

NIST - Room Temperature Conversion of CO2 to CO: A New Way to Synthesize Hydrocarbons

Anyway, the CO2 is storable as LCO2, because it's easy to do so. The CFRP tank can easily withstand the pressures involved. The CO is stored as a gas at 10,000psi, because it will not remain liquid unless it's as cold as LOX and all cryogen tanks require constant cryogenic cooling power. The O2 is also stored as a gas at 10,000psi, for the same reason.

As far as the radiator fan speed is concerned, you need to move a lot of atmospheric mass for the near-vacuum that is the Martian atmosphere to have a significant cooling effect. I don't see a practical way around that problem. Radiative cooling is not used for combustion engines because it's impractical. All Earth-bound motor vehicle engines, whether air-cooled or liquid-cooled, use convective cooling. You can (and should) absorb some of the waste thermal power to heat up the CO2 intake charge and CO / O2, but the engine coolant must remain below what is tolerable by the engine and coolant used. That means a big radiator with a big fan providing convective cooling.

tahanson43206 · 2022-05-01 16:37:43

For kbd512 re #248

Thanks for providing the detailed numbers and scenarios for the topic.

We seem to be hung up with regard to use of LOX as the oxidizer.

Hopefully additional discussion will provide a way forward.

Having a tank at 10,000 psi anywhere near an operating machine seems like a risk not worth taking, but perhaps there are arguments in favor.

If LOX is being consumed by a working machine, I don't see a need to cool it, so perhaps there is an explanation for that feature as well.

Thanks again for adding important details to the flow!

(th)

kbd512 · 2022-05-01 18:12:12

tahanson43206,

Most construction equipment is not being used 24/7. Most mining equipment not related to ore transport on conveyor type systems doesn't see that kind of duty cycle. If you're going to use a conveyor belt, then electrical power input makes a lot more sense. When you fill a tank of liquid or gas whatever, it's temperature will eventually equilibrate to the same temperature as the environment it's sitting in. On Mars (-81°F to 70°F in most places besides the poles), that means over 200°F too warm for cryogenic LOX (-297°F) / LCH4 (-260°F) / LCO (-314°F). Lowering the temperature of any of those substances by over 200°F requires a massive amount of cooling power. Good insulation helps a lot, but warming from the ambient environment is inevitable. LOX/LCO without cooling is use/lose. It's not storable the way Propane or gasoline or diesel are. Diesel (freezes at 32°F) and even gasoline (freezes at -100°F) would have storage problems during Martian night time temperatures (-100°F), unlike Propane (freezes at -306°F).

Edit: Every Toyota Mirai moving down the road contains a pair of H2 tanks pressurized to 10,000psi when they're initially filled with Hydrogen gas.

Last edited by kbd512 (2022-05-01 18:14:40)

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