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Reactivity Controlled Compression Ignition (RCCI) for Simultaneous Reduction of Fuel Consumption, NOx and PM

Researchers at the University of Wisconsin led by Dr. Rolf Reitz are developing a dual-fuel compression engine combustion strategy called reactivity controlled compression ignition (RCCI) to simultaneously reduce fuel consumption and regulated emissions of NOx and PM. (Earlier post.)

The Wisconsin Alumni Research Foundation (WARF) is seeking commercial partners interested in developing the process, and the University has applied for a US patent on the technique. Members of the Wisconsin team—as well as partners at Oak Ridge National Laboratory—will deliver a set of papers on RCCI at the upcoming SAE Powertrains, Fuels and Lubricants Meeting in San Diego in October.

Numerous technologies have been developed to address the need for diesel engines with reduced emissions. However, measures which reduce engine-out NOx production typically increase PM production, and vice-versa (the “soot-NOx tradeoff”). Current technologies and combustion strategies developed to reduce both NOx and soot generation are difficult to implement and control and many still require expensive after-treatment measures.

The RCCI process uses in-cylinder fuel blending with at least two fuels of different reactivity and multiple injections to control in-cylinder fuel reactivity to optimize combustion phasing, duration and magnitude. The process involves introduction of a low reactivity fuel into the cylinder to create a well-mixed charge of low reactivity fuel, air and recirculated exhaust gases.

Examples of fuel pairings for RCCI are gasoline and diesel mixtures, ethanol and diesel, and gasoline and gasoline with small additions of a cetane-number booster (di-tert-butyl peroxide (DTBP).

The level of recirculated exhaust gas and the closure of the intake valve are controlled such that a high reactivity fuel is injected before ignition of the premixed fuel occurs. The high reactivity fuel is injected using single or multiple injections directly into the combustion chamber.

Multiple injections of fuels at different reactivities allow optimization of Premixed Controlled Compression Ignition (PCCI) type combustion in engines, reducing emissions without the need for after-treatment methods. By appropriately choosing the reactivities of the fuel charges, their relative amounts, timing and combustion can be tailored to achieve optimal power output (fuel efficiency), at controlled temperatures (controlling NOx) with controlled equivalence ratios (controlling soot), the researchers say.

Key benefits cited of the strategy include:

  • Lowered NOx and PM emissions
  • Reduced heat transfer losses
  • Increased fuel efficiency
  • Eliminates need for costly after-treatment systems
  • Complies with EPA 2010 emissions guidelines without exhaust after treatment




You are trading complexity for efficiency, and the complexity impacts the users directly (they have to fuel the vehicles).
I can see this working on professionally driven vehicles - trucks buses, vans etc, but I am not sure about domestic cars - UNLESS you make them "fail soft" in that if you run out of one fuel, it can still operate (in a "get you home" or "get you to a gas station" mode) for say 50 miles.

Combine this with a hydraulic hybrid, and you might really have something (but rather complex).


EVs will be much simpler, cleaner and eventually cheaper, specially for domestic cars.


"EVs will be much simpler, cleaner ..."

Depends how the electricity is generated. If its with coal fired power plants its hardly cleaner.

Stan Peterson

The assumption that coal fired external combustion electric generation is necessarily dirty, is essentially a stupid fable. It is produced by the anti-technology ignoramuses of the Green movement, who have or possess or disposed to listen to little technical talent. It comes from the following sources.

1) There are lots of "grandfathered-in" extremely old and obsolescent, coal plants with little or no emission cleanup equipment installed, that are still running.
2) Little or no appreciation of how clean IGCC coal plants can be.
3) Consequently the Green movement doesn't realize that IGCC coal plants run cleaner than Natural Gas plants, and at a higher efficiency. Since they burn "cleaned" created syn-gas, which has toxic components removed, and is cleaner than Natural gas, and can sequester lower temperature exiting CO2, better than any other fossil sources, as well.
4) This is a perverse consequence of the stupidity of the Carter Administration's Faustian bargain creating/forcing these grandfathers via "best-available" upgrade requirements.
5) The "No Nuke" demagogy forcing the cancellation of many otherwise acceptable nuclear plants 20 years ago, along with deserving potential disasters-in-waiting, without discrimination, between good and bad examples.
6) These acceptable Nukes were planned to have provided the power to displace and scrap the "old smoker" coal monstrosities, but never did.
7) These dirty facilities MUST continue to run as there is no other choice available to PUCs or Utilities.
6) Green agitation has forced investment and construction almost exclusively of non Base-load power plants, by forcing "investment" in wind and solar plants which by their nature of operation and economics are exclusively peaking or worse demonstration plants.


This is pretty ingenious though I'm pretty sure I've seen this before (on GCC no less). Selective fuel injection essentially achieves variable compression ratio without some sort of a complex mechanical system.

Electric vehicle motors are three-to-five times more efficient than gasoline-powered vehicles. While it's best to power EVs from renewable energy sources, the efficiency of EVs makes them cleaner, producing less carbon – even when they are charged using coal-fired electricity. This is something "the Green movement" knows full well but the long tailpipe myth is still used as an arguement against EVs by those who...


ai_vin, A heavy-duty diesel engine is, on average, more than 40% efficient in long-haul traffic. The maximum efficiency is about 45%. A passenger car diesel engine is 25% efficient on average but the maximum efficiency is at about 42%. The development potential (including hybridization) could approach 40% in this case too. Coal-fired power plants in the USA are about 33% efficient. Although there is a potential to improve this efficiency as well, the electric motor would have to have a peak efficiency of more than 100% for coal-power to be competitive with future diesel-hybrid powertrains. However, if Peak Coal is about to come soon, we do not even need to bother about the option of coal-power EVs...

Returning to the main topic, I would like to conclude that there are also several other options to reduce emissions and improve efficiency than the one described in this article. Even fairly conventional combustion systems have been demonstrated to be able to meet EPA 2010 without NOx aftertreatment.


Peter XX,

How you can write such statements? Absolute misinformation!!! Where you have seen diesel powered automobiles 45% efficient. Let's calculate on fingers. Diesel calorific value is around 13 kWh per liter. And you are saying that you have seen diesel automobile which consumes 2 l/100 km. Nonsense.
Electric vehicles use on average 12 kWh of electricity per 100 km and they are 90% efficient.

The calculation completely obvious. Never talk such nonsenses ever again. Diesel light duty vehicles are at most 20% efficient. The heavy ones do not differ so much. 45% diesel engine efficiency can be reached at power plant with optimal conditions but in general it is not more that 40%.


I read one of the papers on this technology. It is definitely one to watch. They are seeing peak thermal efficiencies of 54% to 57% depending on the fuels used, estimating averages of 50%. This is better than the best diesel engine. A promising fuel ratio is 80% gasoline, 20% diesel. Doesn't that ratio box nicely with how oil is refined in the US? Think diesel engine architecture, with port fuel injection added for the gasoline. One nice thing is that their diesel injection pressures are only ~500 to 800bar, compared to today's complex 2000+ bar systems. Engine out NOx and PM are low. I see the potential for a robust design with little or no after-treatment, compared to how conventional diesels now have to be configured. There is certainly complexity in the calibration, but not in the hardware, I'd say. I'm not sure the calibration complexity is any more than a modern diesel or SI engine, though.

As mahonj said, coupling this with a hydro-pneumatic powertrain could be pretty exciting. Doing a walk from existing diesel applications and hydraulic hybrid studies, I think a half-ton pickup with a combined EPA of 30mpg and all of the current functionality of existing 1/2 tons would be possible, at a cost similar to a conventional diesel-mechanical powertrain with full after-treatment.


I am absolutely not giving you misinformation! Recall that Rudolf´s first engine had an efficiency of over 20% and this was more than 200 years ago. The engine of the VW Lupo 3L had a maximum efficiency of 45.1% (according to VW Chairman Piech himself). The peak efficiency of the (diesel) engine in my car is 42.5%, so it has some development potential. You can check any publication and find that these numbers are correct! I have reached a fuel consumption of 4.2 l/100 km with my diesel car but the official figure is 4.9 l/100 km. Today, a Volvo S40/V50 has an official figure of 3.9 l/100 km. This is in all cases at an a-v-e-r-a-g-e engine efficiency of some 25%. In a series hybrid, you would operate near the sweet spot, i.e. around 40%. However, the electric drive system of a series hybrid is very inefficient, so a parallel hybrid would be better, although the average diesel engine efficiency would be less than 40% in this case. There is a great potential to improve in this area (hybrid) but to get an average of 40%, you would still have to increase engine efficiency somewhat as well. It is a challenge but not impossible. I do not think, and did not say, that you could achieve 2 l/100 km but 2.5-3 l/100 km does not seem impossible, i.e. less that a factor of 2 of improvement compared to my own car. We already know that the Lupo 3L and the Audi A2 could achieve 3 l/100 km, even without a hybrid drive system. Is that misinformation? The Lupo was small but the A2 was O.K. for 4 people with luggage.

I will not discuss any numbers on EV efficiency this time, but the a-v-e-r-a-g-e efficiency of the electric drive system it is definitely lower than 90%.

Darius, do not ever accuse me of talking nonsense again!


I agree with most of your analysis. However, I think it will be very difficult to get above 50% peak efficiency in a car engine; maybe for a stationary engine or a heavy-duty engine.

I would seriously consider a more efficient hybrid system than an electric hybrid for an ultimately efficient ICE-powered car. Whether this is kinetic, hydraulic or pneumatic, is too early to say. We would need to find the practical limitations for each system first to pick the winner. It is, in any case, bad news for HEVs and on the long term, maybe also for PHEVs and EVs. The problem for the metioned alternatives is that most of the funding is now concentrated on electric drive. We need to get away from the electric drive hype and be more receptive to alternative (and potentially more efficient) options.



Since electricity is work (and NOT A FUEL), an electric motor is a WORK CONVERSION device, NOT an energy conversion device like an internal combustion engine. So comparing a "90%" efficiency (which is a SECOND Law efficiency) to an engine efficiency at 40-50% (a FIRST law efficiency) is quite misleading to say the least.


Best case hybrid/diesel drive train efficiency would be about 40% (over a duty cycle) which is about the same or slightly better than steam reforming (70%) to fuel cell (50%) ~35% overall

Best case EV should do slightly better than this (60% CCGT) and 80% (charging + motor) ~48%

If you were using a series hybrid like the Swift

You would have a 3kWh battery and a 20-30kW range extender. A small range extender would be much easier to use advanced fuel injection technologies, or just make the engine small light and simple.


Let's get out of the pseudo authoritative mode of saying "never say that again". Who the heck do you think you are? We will all decide what is acceptable, no one person has that power.


3PeaceSweet, best CC could get 60% on natural gas but in the coal case, you would have to gasify the coal first, clean the gas etc., so total efficiency will be much less than 60%. Even 50% is difficult to achieve. Recall that current efficiency in the US is about 33%, so there is some homework to do. By putting 50% in your simple calculation, the result would be similar for the cases you compare.

In a well-to-wheel efficiency analysis, there are so many steps that the assumptions and conditions are very crucial. By making these choices, you can get any result you want. I showed you such a case as an example and, of course, many of you do not like the outcome but this is a way to create a debate.

Your famous MIT professor in the USA, J. B. Heywood showed in a well-to-wheel study (link below) that a HEV would be slightly better regarding energy use than PHEV, FCV and significantly better than a BEV. This corroborates what I indicated in a previous comment. Note that the MIT HEV ran on gasoline; the diesel option was not thoroughly evaluated. Electricity generation was US mix of coal and natural gas. The only "problem" I find with the study is that the energy base for the ICE was crude oil, so we do not have the same energy base in all the cases. If we would produce gasoline or diesel from coal (with loss of efficiency compared to crude oil), the electricity options would probably win. So, there is some point in investigating the electric option after all.

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