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SAE REX: PHEVs and REEVs could open door for advanced combustion regime engines

Increased market penetration of plug-in hybrid electric vehicles (PHEVs) and range-extended electric vehicles (REEVs) across vehicle segments could present an opportunity for emerging advanced combustion regime engines, such as those using various low-temperature combustion modes, according to a number of presentations at the SAE 2016 Range Extenders for Electric Vehicles Symposium held last week in Knoxville.

The REEV or PHEV also may present opportunities for more novel power sources such as turbines (Wrightspeed), fuel cell stacks (Nissan) or aluminum-air batteries (Phinergy and Arconic), speakers suggested. The REX symposium was sponsored by Mahle; the organizers were from Oak Ridge National Laboratory and Mahle.

In his introductory keynote, Michael Berube, Vehicle Technologies Office Director, Office of Energy Efficiency and Renewable Energy, noted the importance of both engine and fuel technology in a PHEV scenario.

If PHEVs are going to play a big role, what is the fuel source for that? How efficient will it be? You’re going to need to have very scalable low-carbon fuels if you are going to have PHEVs be a path for deep decarbonization. We certainly believe at DOE that that is a possible path. We don’t have one solution that we are here to say is the right one, but we believe that PHEVs could potentially be a key pathway. But to do that, we need to think about the engine.

High efficiency engines with low-carbon fuels clearly is a major, major pathway. Not the only one. But we believe this a major pathway.

—Michael Berube

Berube went on to reference the importance of DOE’s major new Co-Optima initiative (earlier post), an effort to co-optimize new fuels and light-, medium- and heavy-duty engines which together could achieve very significant performance improvements. Specifically, Co-Optima is targeting a reduction in per-vehicle petroleum consumption by 30% vs. the 2030 base case, which is constrained to using today’s fuels.

In its short life-time, Co-Optima has grown to a 9-laboratory team with more than 130 researchers tackling different aspects of the problem.

We believe that [Co-Optima] is a major, major aspect of how we can achieve these [decarbonization] numbers. We believe that, using both of those together, co-optimizing the fuel and the engine, and combining it now with the overall electrified vehicle, you can get dramatic reductions in the overal CO2 level.

The focus is what fuel properties maximize engine perfromance. What if that ICE is now operating in a very narrow range, powering the electric vehicle?

What I suggest for you, as you think about PHEVs, think about now having very optimized engines, very optimized fuels that have a high level of renewables in those fuels. You now have a low-carbon fuel that can be operated in engines that are operating in a much more narrow band. Within that band, we can get to a very high level of efficiency. There is a very strong case to be made for that PHEV world.

—Michael Berube

In a subsequent talk, Scott Curran from ORNL—one of the organizers of the symposium along with Robert Wagner from ORNL and Hugh Blaxill from Mahle Powertrain—noted that the ability to decouple the engine from the drive cycle, as well as the availability of high voltage current, can help overcome challenges facing advanced engine and emission control systems developers.

The role of the internal combustion engine is changing. We still see a prominent role for these engines moving forward. The ability to refuel large amounts of energy very quickly is going to remain extremely attractive to consumers.

The EPA Tier 3 emissions standards are going to be incredibly difficult to meet. We are going to keep relying on advanced engine technologies to meet these regulations, and as we start looking for higher and higher degrees of electrification, these hybrid systems are going to have to integrate all the opportunities and challenges for the engine, the aftertreatment and the power electronics all to work as one. That’s where things start to get really exciting.

As we look along the spectrum of increasingly electrified vehicles, what is the design space that this increasing amount of electrification opens up to optimizing? As we start to explore this higher degree of electrification, there are going to be some very different design requirements for internal combustion engines.

—Scott Curran

One example of the potential for low-temperature combustion (LTC) engine technology for range extended electric vehicles (REEV) presented at the Symposium was work by Ali Solouk and Assistant Professor Mahdi Shahbakhti at Michigan Technological University.

The category of LTC spans a range of specific technologies; these are of great interest as they promise to improve fuel economy, and reduce NOx and soot emissions by improving the in-cylinder combustion process.

LTC technology faces two main difficulties: first, a narrow operating range, which limits the use of the technology in conventional powertrains; second, complex combustion control, particularly durient transient operations. However, when applied in a range-extending application (i.e., as a generator), an LTC engine can work in a narrow operating area and increases the range of the battery pack.

Souk and Shahbakhti modified a turbocharged 2-liter GM Ecotec direct injection engine to function as a multi-mode LTC/Spark Ignition engine. The LTC modes included homogenous charge compression ignition (HCCI) and reactivity controlled compression ignition (RCCI) LTC engine.

Major changes to the base engine included:

  • design and programming of a new Engine Control Unit (ECU)
  • the addition of a port fuel injection system
  • the capability to adjust intake temperature, pressure, and dilution level through the use of an intake air heater, supercharger, and Exhaust Gas Recirculation (EGR) rate modulation, respectively.

The engine functions as a generator for the battery pack.

Optimization results showed that in the UDDS driving cycle, the single-mode HCCI and RCCI engines offer 12% and 9% fuel economy improvement, respectively over a single-mode SI engine in the REEV. These improvements increase to 13.1% and 10.3% in the HWFET driving cycle. This fuel economy improvement is reduced to 3% in comparison to a modern CI (i.e. diesel) engine in the HWFET driving cycle.

Simulation results showed that the LTC engine offers higher fuel economy improvement in more aggressive driving cycles (e.g., US06) compared to less aggressive driving cycles (e.g., UDDS).

The optimal control algorithm enhanced the fuel economy by 17.0% over the rule-based strategy in a hybrid electric vehicle integrated with an LTC engine.

Using a “multi-mode”—i.e., both HCCI and RCCI—instead of “single-mode” LTC engine in the REEV provided 2% more fuel economy improvement, depending on the type of the driving cycle. Reducing the mode-switching fuel penalty increased the fuel economy improvement beyond 2%.

Among the LTC modes, HCCI was the dominant engine operating mode. If the fuel penalty to the RCCI mode decreased by 95%, the engine operated near to 45% of its ON time in the RCCI mode.

The study also found that HCCI and RCCI were more favorable from the NVH considerations, compared to the SI engine. This is due to use of low engine speeds in the LTC modes.

The team will be presenting a new paper on their work at the SAE 2017 World Congress next year.


  • Ali Solouk, Mohammad Shakiba-herfeh, Kaushik Kannan, Hamit Solmaz, Paul Dice, Mehran Bidarvatan, Naga Nithin Teja Kondipati, Mahdi Shahbakhti (2016) “Fuel Economy Benefits of Integrating a Multi-Mode Low Temperature Combustion (LTC) Engine in a Series Extended Range Electric Powertrain” SAE 2016-01-2361


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Hybrid plugin cars will not play any future role because driverless BEVs are a reality in about 12 months from today. Driverless BEVs can do over 100.000 miles per year as taxies and at lower cost per mile than any car that uses a non-durable gas engine that also uses expensive gas and is expensive to maintain relative to a BEV.

Musk has confirmed that he expects Tesla to ready its fully driverless software by the end of 2017. At that time will be uploaded to over 150.000 Teslas with the needed hardware and they will start to collect data on the safety of this fully self-driving system. Drivers will still be required to monitor traffic and be ready to take over not because it is needed but because the law says they must. However, that will be a temporary situation. The plan is that when enough evidence is collected to convince authorities that Tesla’s fully self-driving system is much safer than the human driver the authorities will approve the system for hands free full self-drive. Also Tesla can start selling cars without human controls to people without a driver license. I will be very surprised if we don’t see fully self driving Tesla taxis on the Tesla Network by the end of 2018.


In principle, this is the same futile and despairing effort copying Mercedes blowing billions out of the window in R&D for 5 new ICEs. They'd have been far better off investing that money, time and effort in electric drive trains.
All these useless innovations appearing nowadays would have been acceptable decades ago. But in the past they had no competition to fear from electrons. Now they're attempting everything possible to extend their useless technology that has no future.


BEV's are blindly advocated by many without considering the reality: the fuel isn't green or efficient. In most of the US, the electricity generation is by coal or natural gas. If produced by the newest, most efficient gas turbine, the efficiency at generation is aprox 50%. Then comes the line losses. The electricity may be transmitted hundreds of miles. Overall, its more efficient to burn the natural gas in the vehicle. Even more so if the vehicle is a hybrid.

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Nordic you are an ignorant who live in an imaginary reality. Coal is going out fast in the us being replaced by gas and renewables. Renewables already made up over 50% of new electric generating capacity on a global scale. The transition to a renewables co2 free grid is accelerating. Also Tesla will soon not only sell you a BEV but also a solar power plant to make all the electricity you need for your cars and everything else.


Henrik, no insults.
Coal will be with us along with natural gas for a while IMO.
I can have an opinion without criticizing nor insulting people.

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SJC I know it is insulting and maybe I shouldn’t. But it is the truth and I am still a saint compared to Trump and Clinton and they kind of set the level of acceptable public communication. I am sick and tired of people like Nordic and quite frankly I feel good about insulting him. The world has changed. Old fashioned politeness is becoming rarer and I admit I may also leave it completely behind.

Below is a link that shows how fast coal is disappearing from the US grid. It is already lees than natural gas.

Dr. Strange Love

In general, Electricity is not clean. Coal/NG from source to target is maybe 30-35% at best. HEV platforms like the current Prius already top this. Efficiencies and Emissions will only get better.

Henrik: Listen ... COPPER is expensive. It will only get More expensive with the rollout of more Electric platforms and infrastructure to support it. Go rant about something else.

Here's a Man's sport, the ultimate stress relief. No Autonomous Vehicle Required. Enjoy.

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The world made 18.7 million ton of new copper in 2015. One million ton is enough to make 20 million self-driving Tesla BEVs that can replace 140 million non-self driving gassers. And copper can be fully recycled.

Copper may be expensive but it is not a show stopper for BEVs.


The new President will make America Great Again. He may even make America clean, employed and rich rich again by 2024 or so?

The switch to clean electricity and clean electrified vehicles is part of a new industrial/technical revolution and will not stop.

ADVs is part of near future ground transport normal evolution and will become common place by 2030 or so.

Clean energy from REs such as Solar and Wind (with storage) will become major energy sources by 2030 or so.

Who will do it first? Norway, Japan, UK and Germany are the current leaders. USA and China will follow.


Dr. Strainge Love,

In case applying same principles as for electricity generation Prius efficiency 29%. And it not "topping" power generation which can use any fuel including nuclear and renewable. Other figures are just Toyota marketing stuff.

Gasoline calorific Value
11,8 kWh/kg
0,755 kg/l
8,909 kWh/l

Prius ratings EPA (wikipedia)
km kWh
21,26 8,909 Gasoline consumption
100 41,90498589
Efficiency 29% Calculated based on electricity estimated

160,9 25,9 electricity consumption
100 16,09695463
Efficiency 75% Estimated


Did you read the emissions report on comparing EV to current light duty fleet? The EV had roughly half the emissions. But, the current fleet rating is 22 MPG, so not a very accurate comparison. The EV is a small and expensive car. The new EV is a state of technology vehicle as compared to antiquated fleet. Just nonsense comparison. One of the commentators said a better comparison would be a new Prius. The Prius achieves more than double the fleet average for mileage, so it would have less emissions than the EV. If one filled the Prius up with E85 the emission would drop another 30%-60%. Probably a rating in which the grid will never catch up. Fill the Prius up with what many expect cellulosic to achieve and the grid could not possibly catch up even if entirely wind, solar, hydro, and nuclear. By the way, we should all be minimizing power on the grid so the green portion can achieve a higher percentage of pollution reduction. This is just common sense.



In this case I do not read. I make very simple common sense calculations, which I do for power generation. Prius gasoline to wheels efficiency is 29% in comparison of 75% electricity to wheels. That is pure fact without any exceptions. It means fuel efficiency is 2,6 fold (precisely) more.

In order to compare apples to apples we assume Prius electricity to wheels efficiency 100% then respectively gasoline to wheels efficiency will be 38%.

In that case taking into account electricity transmission losses 10% the competing power generation efficiency (heat cycle) shall be more than 42%. Lets say it is lowest possible efficiency of new thermal power stations including coal.

When you taking into account existing aging coal power generation with 30% efficiency and 50 MPG most advanced vehicle you can get different result especialy for "coal states".

"If one filled the Prius up with E85 the emission would drop another 30%-60%".

To consume food for fuel not good solution taking into account limited resource. To make cellulose ethanol different story. But here again you could more easy combust cellulose (wood) waist, generate electricity and make guaranteed reduction of emissions by 80%. So electricity path is better in any case from emissions point of view and liquid or other fuel is better in case electricity do not work. I support range extension paradigm since liquid fuel has big advantage on unlimited range and fueling infrastructure availability but not from emission point of view. Therefore I believe ICE will be only range extender as such in combination with battery and electric motor. Voltec creators believe it should have all functionality of regular ICE. I do not think so and in general I supporting article idea.

"By the way, we should all be minimizing power on the grid so the green portion can achieve a higher percentage of pollution reduction. This is just common sense." Why??? What is the point??? BEV use mostly night time electricity and has very good power consumption evening effect while reducing electricity loss percentage, increasing grid and generator utilization, power price and in the end emissions and air quality. It is valid even for current electricity generation mix.

To make power generation clean is very easy and has been done my some countries many many years ago. Largest one is France. Most of professionals in private would tell you that nuclear during life cycle has 10 times less carbon emissions than wind or solar. But in public nobody will speak because being afraid killed by greenbacks. I think when this nuclear which hunt will be over the nuclear will restart once again.


P.S. I made mistake. BEV's reducing power price.



Nothing really wrong with how clean nuclear energy is. It is just a question of comparative cost per kWh produced and sold.

Recent NPPs take 12+ years to build and produce clean electricity at about $0.22/kWh vs less than $0.10/kWh for REs with storage. REs are normally built in about 2 years. Secondly, a very high percentage of nuclear energy produced is not used on a 24/7 basis, especially during low consumption periods, weekends and holidays. Massive storage and/or NG standby power plants would be required to use close to 100% of the energy produced by NPPs. About the same if not more than for REs?

Dollar for dollar, USA (and most countries) will be financially better off with clean REs (Hydro + Wind + Solar) + a few up to date NGPPs + storage units to handle peaks.

Lower cost, higher performance wind and solar farms together with lower cost near future storage units could reduce REs cost close to 5 cents/kWh by 2025 or so. If so, NPPs and CPPs will both be wildly over priced and abandoned.


Are you not suspicious about such cost indication? Do French people are completely stupid or unimaginably rich?

In reality new nuclear power price is around $0,05/kWh to $0,06/kWh.

Concerning power generation cost please google and download:
Program on Technology Innovation: Integrated Generation Technology Option

(Electric Power Research Institute)

For new power generation guys I would tell that commercially wind or solar power is better since it is much less commercially risky and requires very small financial exposure. But power price will dramatically increase due to solar or wind power like it happened in Germany. The power storage solutions are needed as well as long as share of wind or solar passes 20% share of overall power generation mix. Power storage infrastructure cost is huge and power losses during storage procedure are no less than 30%. Therefore not regulated and not disconectable power sources like wind power incur huge cost in other power system values chain parts. But for private business and entrepreneures renewables are very attractive due to small financial exposure and positive public opinion.

On contrary:
1. Nuclear power suffer from prohibitive NRC regulations which double not only construction cost but incur uncertainty for construction process duration. 12 years might be not an issue. Uncertainty is an issue.
2. No research programs finance from US government or any other western government apart from South Africa. In general everything in US was terminated after 1986. No new design or fuel (like UN) application during recent 30 years. No nuclear waist application programs.
3. Nuclear power suffer from public mass hysteria although nobody died or even got sick since 1986 former USSR Chernobyl accident in oposit to coal or even gas based power generation. Coal miners die every day and lung disease due to emissions are quite common. Wind power noisy and solar power polluting a lot during manufacturing. Ask question why Ukraine both government and public are supporting new nuclear power development? Chernobyl located in Ukraine.


Darius....please double check the real price of electricity from recent NPPs being built in UK and Finland. Your claimed $0.05/kWh will turn to almost $0.22/kWh?

The lowest cost NPPs are probably being built in China but it is difficult to obtain the real total cost.


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