RS-68 and RS-25 don't count as they are LH2/LOX engines.
The RD-180 has similar ISP (SL,VAC) to Merlin 1D
Is there a GG kerolox engine that outperforms Merlin? I can't name one.
Quote from: DOCinCT on 05/10/2017 03:12 pmThe RD-180 has similar ISP (SL,VAC) to Merlin 1DWrong. It has over 25, almost 30 seconds better isp.
Quote from: Kaputnik on 05/09/2017 10:19 pmIt's remarkable that Elon thinks engines are their weak point- the Merlin has outstanding T:W, impressive isp, and they churn out more of them than any other engine builder.It's the structures that have caused their LOVs so far- the engines have had a good track record.isp of merlin is the worst of all liquid fueled rocket engines used in any orbital-capable rocket in USA today.RD-170-derivates used by Atlas and Antares, RS-68 used by Delta, RS-25 that will be used by SLS all have considerably better isp.
It's remarkable that Elon thinks engines are their weak point- the Merlin has outstanding T:W, impressive isp, and they churn out more of them than any other engine builder.It's the structures that have caused their LOVs so far- the engines have had a good track record.
Quote from: hkultala on 05/10/2017 05:20 pmQuote from: DOCinCT on 05/10/2017 03:12 pmThe RD-180 has similar ISP (SL,VAC) to Merlin 1DWrong. It has over 25, almost 30 seconds better isp.If any engine has proved the folly of ISP measuring, it would have to be Merlin.
Quote from: Kaputnik on 05/10/2017 04:51 pmIs there a GG kerolox engine that outperforms Merlin? I can't name one.doesn't matter.Is there a biplane faster than polikarpov I-15? I can't name one.Still there are lots of aeroplanes much faster than polikarpov I-15, and polikarpov I-15 could not have been considered a fast aeroplane for the last 75 years.
Quote from: hkultala on 05/10/2017 01:40 pmQuote from: Kaputnik on 05/09/2017 10:19 pmIt's remarkable that Elon thinks engines are their weak point- the Merlin has outstanding T:W, impressive isp, and they churn out more of them than any other engine builder.It's the structures that have caused their LOVs so far- the engines have had a good track record.isp of merlin is the worst of all liquid fueled rocket engines used in any orbital-capable rocket in USA today.RD-170-derivates used by Atlas and Antares, RS-68 used by Delta, RS-25 that will be used by SLS all have considerably better isp.And yet, here it is, powering the F9 to orbit, launching payloads cheaper than anyone else, returning the booster and landing it, unlike anyone else.It may be the worst liquid fuel rocket - but just look at what it achieves. More than any of the other engines quoted are doing.The engine is a triumph of pragmatism.
...the lowest $/performance of any engine..
Quote from: hkultala on 05/10/2017 05:26 pmQuote from: Kaputnik on 05/10/2017 04:51 pmIs there a GG kerolox engine that outperforms Merlin? I can't name one.doesn't matter.Is there a biplane faster than polikarpov I-15? I can't name one.Still there are lots of aeroplanes much faster than polikarpov I-15, and polikarpov I-15 could not have been considered a fast aeroplane for the last 75 years.The point of this whole diversion was that I was surprised that Elon considers SpaceX to be weak when it comes to engines.The only type of engine they make is a GG, so that is all we can judge them by. Does it stand judgement against its peers? Hell yeah, it's perhaps the best example of a GG engine that we can find. To me that suggests that they are pretty good at building engines.If their GG engine was inferior to other engines using the same prop and cycle, then I would agree that they suck at making engines.Perhaps what Elon is alluding to is that they are weak when it comes to engines running on different cycles or propellants. Hardly surprising given that they have yet to finish developing one.
Higher density fuels have a higher Impulse Density because Impulse density is basically the propellants Specific Impulse multiplied by it's density.
So how is impulse density defined?Weight of fluids and engine/weight of engine?Thrust/weight of engine?
Quote from: rsdavis9 on 05/11/2017 10:41 amSo how is impulse density defined?Weight of fluids and engine/weight of engine?Thrust/weight of engine?Force per flowrate? which give Newton Seconds per Kilogram? Not sure that is any different than ISP.Though I suppose if you want a definition that Merlin wins at maybe Force per volumetric flow rate.
Quote from: DanielW on 05/11/2017 01:59 pmQuote from: rsdavis9 on 05/11/2017 10:41 amSo how is impulse density defined?Weight of fluids and engine/weight of engine?Thrust/weight of engine?Force per flowrate? which give Newton Seconds per Kilogram? Not sure that is any different than ISP.Though I suppose if you want a definition that Merlin wins at maybe Force per volumetric flow rate.There really doesn't need to be a definition at what the Merlin 'wins' at - just look at the accomplishments of the whole system. Those are wins all the way down.
isp of merlin is the worst of all liquid fueled rocket engines used in any orbital-capable rocket in USA today.RD-170-derivates used by Atlas and Antares, RS-68 used by Delta, RS-25 that will be used by SLS all have considerably better isp.
I have not seen an ISP figure from SpaceX since the first version of the Merlin 1D. Since then we have seen a 26% increase in thrust. Now I am not a rocket scientist, but as I understand, increasing thrust requires either larger throat or higher ISP. I have no reason to believe the throat or other physical dimensions of the Merlin 1D have changed so I believe the ISP has gone up a lot.
Quote from: Roy_H on 05/11/2017 06:04 pmI have not seen an ISP figure from SpaceX since the first version of the Merlin 1D. Since then we have seen a 26% increase in thrust. Now I am not a rocket scientist, but as I understand, increasing thrust requires either larger throat or higher ISP. I have no reason to believe the throat or other physical dimensions of the Merlin 1D have changed so I believe the ISP has gone up a lot.probably just higher chamber pressure which translates to higher exhaust velocity which is ISP.
Quote from: rsdavis9 on 05/11/2017 07:35 pmQuote from: Roy_H on 05/11/2017 06:04 pmI have not seen an ISP figure from SpaceX since the first version of the Merlin 1D. Since then we have seen a 26% increase in thrust. Now I am not a rocket scientist, but as I understand, increasing thrust requires either larger throat or higher ISP. I have no reason to believe the throat or other physical dimensions of the Merlin 1D have changed so I believe the ISP has gone up a lot.probably just higher chamber pressure which translates to higher exhaust velocity which is ISP.Increasing chamber pressure will improve ISP a little but the trouble is with a GG cycle you spend more propellant in the gas generator to provide the increased power to the pumps which does not contribute to thrust. The big gains would be if they were able to improve pump efficiency and GG turbine efficiency. Has anybody tried to back-calculate ISP from those simulations of F9 flights?