Fuel, Emission Science Review of Dipetane
Dr Stephen Dooley
Assistant Professor of Energy Science School of Physics
Trinity College Dublin, the University of Dublin
+353 1896 2030
I have been asked to review a body of literature on the effectiveness of Dipetane in improving engine and boiler combustion, including an assessment of the "non-additive" nature of "Dipetane Fuel Technology". My analysis is simply summarised: Dipetane does appear to result in an increase in fuel efficiency of approximately 4.5-15% in most instances. That is, vehicles using Dipetane appear to travel further on the same quantity of fuel than those not using Dipetane. This is accompanied by a reduction in soot and unburned hydrocarbons in the exhaust gases studied, mostly for diesel or other diffusion/mixing limited combustion device configurations, such as boilers.
It is accepted combustion science that the efficiency of diesel mode combustion devices is limited by fuel/air mixing. These findings are therefore consistent with a theory of Dipetane affecting an enhanced mixing of fuel with air, allowing more complete combustion to occur, thus producing efficiency gains. Accounted below are details of my observations, analysis and opinions from my reading of the documents supplied to me. Summary of Validity of Dipetane Testing & Promotional Materials Twenty-one separate promotional leaflets and brochures stating the benefits of the use of Dipetane have been reviewed with regard to their scientific legitimacy. The claims made in the promotional materials are supported by the information contained in a series of technical documents that describe the material and combustion properties of Dipetane, and its operation in a series of compression ignition engines, spark ignition engines and in diffusion flame boilers. Importantly, from chemical analysis data of Dipetane it is clear that Dipetane is a non-additive fuel technology, it's chemical composition is typical of the composition of liquid transportation fuels.
The evidence provided by these technical documents is summarised below. The validity of the evidence with regard to the state-of-art in fuels, combustion and emission science, in the opinion of the author, is also stated. With the information of these supporting technical documents, a summary briefing note on Dipetane dated April 2017, "Dipetane Technical Summary", is also examined. Dipetane claims to allow the fuel to be burned more completely by enhancing the interaction of the fuel with oxygen contained in the air. The arguments presented pertaining to the problem to be solved by Dipetane are certainly very consistent with the scientific consensus in the international combustion research community.
Moreover, the claims stated in the twenty-one items of promotional material are, in general, supported by boiler or engine combustor measurements of power, fuel consumption, oxygen and/or emission data described in three principal reports:
- "Dipetane in Engines"
- "Dipetane in Boilers"
- "Eolas Report"
The contents and validity of the "Dipetane Technical Summary (April 2017)" and of Reports 1-3 are reviewed in detail below. These claims are also supported from the lay perspective by a large body of testimonial letters from; government organisations, transportation companies and logistics companies. These testimonials are listed in Appendix I and contain the opinions of users of Dipetane over extended durations. The testimonials are unanimous in endorsing the benefits of using Dipetane to; engine lifetime and maintenance costs, vehicle mileage, and road worthiness assessments. In as far as can be judged, these testimonials appear to be genuine, and from reputable organisations. Moreover, these views are consistent with the findings described in the technical reports as reviewed below.
Review of "Dipetane Technical Summary"
It is beyond any scientific doubt that both historical and modern engine-technology/fuel¬technology partnerships fail to extract even a majority share of the fuel chemical energy into energy available for transport . In this regard, the claims regarding the use of Dipetane certainly have a scientifically and societally valid existing technical goal — to improve engine combustion. The document claims that the use of Dipetane allows for less frequent replacement of fuel injectors, diesel particulate filters (DPF) and other power-train components. The failure of these devices is principally due to carbonaceous deposits produced by incomplete combustion of fuel. Again, these are very legitimate goals. Perfect diesel mode combustion requires the perfect mixing of an injected liquid fuel into a high pressure air environment.
The composition of air is 21/79 mole% 02/N2. If this is not achieved within about a few milliseconds, the combustion chemical reaction starts to occur in less that the required amount of air. This produces particulate matter (aka "particulate" or "soot" or "smoke"). The result of particulate production is not just a large loss of efficiency, (lower miles per gallon of fuel), but also the creation of engine deposits which are very troublesome for both engine lifetime and maintenance costs.
This is the simple scientific explanation for what is described in the Dipetane promotional materials as "standard fuels have not been able to get the fixed 21 units of oxygen to access the volatile carbon chains at the point of combustion". Beyond doubt, any increased production of particulate matter will lead to an accumulation of the material in diesel particulate filters and in the engine block; this can lead to lower engine power due to a reduction in the volumetric flow rate of fuel/air through the engine.
Any technology that reduces the extent of soot production will have large advantages to the engine efficiency, cleanliness, and to fuel economy.
Examination of Biofuels Claims
It is true that EU legislation allows up to —7% biofuels to be mixed with petroleum derived fuels. In fact, due to the EU Biofuels Directive  it is law in each member state to include 5.75% of biofuels in all market fuels by 2010, and 10% by 2020. Biofuels are typically oxygenated hydrocarbons to various degrees of oxygenation.
It is well established that fluid properties of fuels that are critical to mixing, such as viscosity, lubricity and vaporisation energy are inferior in the case of biofuels to the case of conventional petroleum derived fuels. Due to this, one can expect the use of biofuels in diesel engines to result in poorer mixing with air relative to diesel. This could in principle produce an increase in particulate matter (soot).
Examination of Ash Claims
"Ash" is metal oxide formed by the normal combustion of metal atoms that are common components of engine lubricating oils. Ash from phosphorus and sulphur can be expected from most lubricating oils. Ashes are troublesome to the engine as they are solids that condense on the diesel particulate filters, see Figure 1. "Soot" (also known as "particulate matter" or "particulate"), is large molecular weight polyaromatic hydrocarbon formed by the incomplete combustion of fuel. Soot also condenses on the diesel particulate filter; this is the purpose of the filter. However, the effectiveness of the filter can be lessened due to the combination of soot and ash.
While the ash formation can only be prevented by removing the metals from the engine oil, the soot formation can be prevented by promoting the complete combustion of fuel to carbon dioxide and water, which are gases, rather than soot which is a solid. The briefing note highlights the interaction of soot and ash. The ability of Dipetane to reduce soot formation will lessen the compounding interaction between ash and soot.
Examination of Urea Claims
For the last several decades, the European Commission and the United States Government have introduced incremental legal requirements for clean ground transportation energy [2-4]. Vehicle manufacturers have realised that it is more cost effective to clean the exhaust gas following combustion rather than engineer reaction conditions that result in the fuel being completely burned in the engine. This is the purpose of both the diesel particulate filter and selective catalytic reduction technologies (catalytic converters). These are sold with every engine in every vehicle in the EU, and most other 1st world countries.
These systems are typically as expensive and as heavy as the engine itself. This obviously adds to the production and fuel operating costs of the vehicle. Urea is used in these devices to remove oxides of nitrogen formed by the poor combustion of the fuel. NO and NO2 (NOR) are harmful pollutants and legislated to be produced at no more than 60-280 mg/km from 2009 (Euro V)  and 60-125 mg/km from 2013 (Euro VI) . The catalytic converter removes the NOR by reacting it with ammonia, NH3. Ammonia is produced on-board the vehicle from urea, NH2CONH2. The more NOR that is produced by the engine, the more difficult it is for the catalytic converter to remove all of the NOR. To evaluate the claims made by Dipetane with regard to passing emissions tests and reduction of NOR, it is necessary to understand this basic science of the exhaust gas after treatment system, but also the basic science of NOR formation. In a basic way, there are two methods by which NO and NO2 can form. The first, commonly known as "Thermal NOR", is by the thermal decomposition of the nitrogen (N2) contained in the air.
This occurs at very high temperatures due to the combination of the compression stroke of the engine, and the propagation of the flame within the engine. This is indicated in Figure 2. The second is due to incomplete combustion of the fuel and is referred to as "Prompt NOx", also known as "Fenimore NOx" . If the fuel does not perfectly mix with the air, the very reactive "CH" species forms from the decomposition of the fuel, and produces NO by the reactions:
- CH +N2 <=> HCN +N (Reaction #1)
- N+O2<=>NO+O (Reaction #2)
The ammonia and expensive metals in the catalytic converter combine to convert the NOx to N2 by the reaction;
- NH3 + NOx <=> H2O + N2 (Reaction #3)
If the fuel and air can be properly mixed, the "prompt" NOx formation will not take place. This will lead to a cleaner operating engine. The benefits of this to the owner would be; non-failure of vehicle emissions tests, prevention of maintenance of engine-catalytic converter, in principal the redundancy of the exhaust gas after treatment system. Therefore, it is logical to suggest that the ability of Dipetane to enhance the mixing of fuel with air should provide a reduction in NOx production and therefore a reduction in the effort required to clean the exhaust gas.
Review of "Dipetane in Engines"The document, "Dipetane in Engines" states a series of claims concerning the benefits of using Dipetane in diesel and gasoline engines. These include:
- Increase fuel efficiency by 10%.
- Reduction of smoke emission by 50%.
- Reduction of greenhouse gas emissions by 25%.
The document is full of testimonials and information gathering reports on the use of Dipetane in diesel and gasoline engines, see Appendix I. The diesel combustion mode is inherently poorly mixed by its nature and consequently suffers from particulate, CO and other unburned hydrocarbons which are certain greenhouse gases, see Figure 2. These are due to poor mixing of the diesel fuel with air in the combustion chamber. Accompanying these products of incomplete combustion will always be a loss of device efficiency due to the inability of the engine to convert the fuel to carbon dioxide and water. Thus, it makes scientific sense that Dipetane ought to be more effective in the diesel engine configuration, rather than in the premixed gasoline configuration where the principal issues are knocking and NOx emissions, which are not mixing limiting phenomena.
The balance of the user experience summarised in "Dipetane in Engines" is consistent with this combustion science hypothesis as —80% of the claims made pertain to the use of Dipetane in diesel engines. The report shows that Dipetane has been characterised as a chemical by the SGS laboratory. I have personal experience or familiarity with many of the test methods utilised. Each laboratory test appears to be well performed and the results correlate with each other with regards to what I would expect for a typical petroleum derive fuel component. It is then not surprising that Dipetane is found to be fully compliant with BS EN 590: 1999 which was the European standard for market diesel fuel at the time at which the test was perform. From the data presented, I confidently speculate that Dipetane will be compliant with the very latest version of these continually refined standards, and indeed with the EURO VI fuel regulations for diesel fuel. I note that Dipetane carries an indemnity against public, products and pollution to a total value of €2,600,000 in anyone year, and that no claims have ever been lodged to the insurance broker over a long period, going back to 1992.
Below I present an essential summary of the various emissions tests accounted in the document. In each case, from the information presented the tests do appear to be carefully and objectively performed and reported.
Linfox Transport, Australia, 2000
The performance of two 1994 FLC 112 Mercedes Benz Diesel vehicles was assessed before and after the use of Dipetane over a period of 8 months. The maximum reduction across each of CO2, CO, NOx, SOx and smoke was reported following test at idle and 2000 rpm. The data show significant reductions in these pollutants, with maximum respective reductions of 23%, 9.5%, 35.4%, 26.8% and 61.5% after the use of Dipetane than before.
Gough Gough and Hamer Ltd, Australia, 2002
Dynamometer tests were performed on a year 2000 Diesel truck with the objective of determining fuel consumption per unit power before and after the use of Dipetane over a 5 month trial period. The baseline test established an average fuel consumption rate of 18.9 gallons per hour to return an average of 331.9 horse power at the wheel across an engine speed range of 1400-1790 RPM. The same test was repeated after 5 months of Dipetane usage. The average fuel consumption was 19.0 gallons per hour returning an average horse power of 356.1 at the wheel. This corresponds to a 7.3% increase in fuel specific horse power due to the use of Dipetane.
Peterbilt Trucks, 1990
A field trial of eight Peterbilt trucks equipped with Cummins 365 Diesel engines was undertaken between December 1990 and November 1992. The average miles per gallon (Mpg) was measured for eight trucks, four trucks each operating with and without Dipetane, at identical three-month intervals of time. The miles travelled was indicated by the measurement of vehicle axel turns with an infrared laser encoder similar in my experience to that used to measure engine speed in engine test-cell situations. The average fuel consumption of the control group is correctly determined to be —4.83 Mpg (4.84 Mpg precisely).
These findings are quite consistent across the measurement series as indicated by a standard deviation from the mean of 0.15 Mpg. This can be taken as an indication of the variability (or the uncertainty) in the determination, that is, 4.84 + 0.15 Mpg or + 3.2%. This is excellent consistency and establishes a fair baseline of truck performance without Dipetane. The data from the test group of trucks operating with Dipetane show a very consistent average fuel consumption of 5.52 Mpg ± 0.14 Mpg, ie. ± 2.6%. Two things are notable here. First, the statistical behavior of the data of the Dipetane test group to the data of the control group is very similar. This is apparent by a very similar distribution about the mean, ± 0.15 Mpg vs. ± 0.14 Mpg. This is what should be expected for tests performed consistently and fairly. Second, vehicles using Dipetane clearly show a larger number of miles travelled per gallon of fuel than those not, 5.52 Mpg vs. 4.84 Mpg, respectively. This corresponds to a fuel saving of 12.65% due to the use of Dipetane. This analysis assumes that both sets of trucks behave equivalently, as is apparent from the statistical analysis of the data.
As a final note, though NOx and CO2 emissions were not measured in the Peterbilt trial, the claim that NOx reductions of up to 40% and CO2 savings of up to 25%, as stated on the flyer, is generally in-line with the emissions measurements reported in other studies available in the "Dipetane for Engines" document. From the Peterbilt trial, one can certainly expect CO2 savings that are commensurate with the miles per gallon savings, the order of 12.5%.
Automobile Test Parts Center, Gongzhou, China, 2015
The fuel economy, litres fuel per 100 km travelled, of five city buses operated by the Baishan Bus Company, China, with Dipetane added to the normal operating fuel was measured over a 7 day period. The performance of each vehicle with the use of Dipetane was compared to a baseline established over the preceding 1 month period. For each of the five different buses tested, the use of Dipetane resulted in an improvement in fuel economy of, 9.63%, 15.22%, 9.98%, 8.97% and 9.10% respectively. These figures quote the lowest fuel economy recorded in the testing of each bus, which was typically observed on the last day of testing.
They therefore represent the maximum benefit experienced. Having analysed the data carefully, in my view it is fair to quote the maximum benefit experienced. This is so as each data set is small, being gathered only over seven days of testing and variable ranges of 90¬600 km per day, it shows continuing improvement and does not reach steady sate, see Figure 3. The exception to this is bus # 7-79148, where fuel economy data for a 1 week "cleansing" period at 600 km/day is also provided. The data show that continued improvements in day-to-day fuel economy are noted in each of the seven days. This would indicate that it takes time for the Dipetane fuel treatment to totally replace the normal fuel; coating of the fuel handling and engine apparatus etc. Figure 3 presents the normalized fuel consumption for each bus with days of use. In all cases the data show a continued improvement in fuel economy with consecutive days of use, up to and beyond at least 3-4 days.
Taking the average fuel consumption for each bus (rather than the lowest as above), for each 7 day period, the use of Dipetane resulted in an improvement in fuel economy of 8.19%, 9.33%, 7.82 %, 6.65% and 8.59% respectively for each bus. These values can be regarded as the worst case benefits observed.
Automotive Testing and Development Services Inc., California, USA, 2002
The performance of a Dodge RAM 2500 pick-up truck equipped with a 5.9 L Cummins diesel turbo-charged engine operated on, diesel, B-20 (20% biodiesel, 80% petrodiesel) and B-20 treated with Dipetane was studied. NOx, particulate matter (soot), unburned hydrocarbon and carbon monoxide emissions were measured in rolling road dynamometer testing representative of California driving conditions. It is well established that the use of biodiesel in compression ignition applications results in higher NOx emissions when compared to petrodiesel.
The study specifically investigates this question for Dipetane fuel treatment, but concludes no reductions in NOx due to the addition of Dipetane. However, the study does note a reduction in both CO and particulate matter, as noted in the other studies documenting the use of Dipetane with regular, petro-diesel. This is again consistent with a theory of Dipetane effecting an enhanced mixing of fuel with air.
NCT Test Results, IrelandThree accounts of failed NTC reports are presented with passed NTC reports apparently due to the use of Dipetane, for sometimes very short durations. Numerous Reports from Distribution Companies Many testimonies from reputable businesses on the benefits of Dipetane to their organization are provided. These are briefly summarised as:
- Coca-Cola bottlers Ireland: 7.94% reduction in fuel costs due to Dipetane usage.
- Irish Defence Forces: 13.6% decreased fuel consumption due to Dipetane usage.
- Courier diesel trucks in Chile: 9 % reduction in fuel consumption.
- Sealink diesel ferries in New Zealand: a 6% reduction in fuel consumption.
- School bus diesels in the United States: a 15% reduction in fuel consumption.
- Distribution company in New Zealand; an 8% reduction in fuel consumption in practical tests.
Review of "Dipetane in Boilers"
This report includes the University of Ulster Research and Consultancy Services Report -"Investigation of the Characteristics of Gas Oil Treated with Dipetane by Means of Controlled Tests of a Domestic Oil Fired Boiler"
The use of Dipetane in a gas-oil fueled burner is studied. The boiler thermal efficiency was monitored in accordance with BS7190. Oxygen, carbon monoxide, sulphur dioxide, nitrogen monoxide and nitrogen dioxide are also measured. The thermal energy generated due to the boiler operation is also measured.
These measurements tell the user how well the boiler-fuel partnership converts the chemical energy stored in the fuel to usable heat energy. 100% thermal efficiency is a practical impossibility in all combustors. This is due to the non-isentropic nature of heat transfer which ensures that there will always be parasitic heat losses away from the intended working fluid.
Also, incomplete combustion is very usual in most boilers and engines owing to a myriad of physical and chemical factors which lead to operational difficulties in achieving complete combustion. If the complete combustion of the fuel with air can be promoted in some way, the thermal efficiency of any combustor will increase, allowing less fuel to be consumed to produce the same work. A metric of mass of fuel (grams) per unit power (kWh) is a valid diagnostic term with which to determine any enhanced efficiency due to the use of Dipetane.
The premise of Dipetane operation is that it allows the fuel to be completely combusted in a quantity of air by enhancing the mixing of the fuel with the oxygen constituent of air. If the fuel were not fully combusted, a larger quantity of fuel would be required to generate a set quantity of energy. Thus, by ensuring the fuel is fully combusted, the minimal amount of fuel is required to generate a specific quantity of energy. This is the nature of the specific fuel consumption term (SFC, g/kwh) used in the report.
The precision and accuracy of the equipment used to make the measurements is better than sufficient to allow for the intended analysis. Baseline measurements of 3% 02, and 6 ppm CO are noted for when the boiler is operated on regular gas-oil. Twenty-one separate measurement sets were performed on the boiler over a 275 hour testing period. The gas-oil was then combined with Dipetane at a ratio of 200:1. Over the next 761 hours a further twenty-three tests were performed.
The most important data reported is the specific fuel consumption. This is a composite of the measured fuel flow rate and the measured power. The accuracy of the power measurements is testified by a calibration certificate for the power meter apparatus employed.
These measurements allow for the important finding that the specific fuel consumption is approximately 10% lower when the fuel is treated with Dipetane relative to when it is not. This can also be stated as, the specific power output is 10% higher when the fuel is treated with Dipetane relative to when it is not. This conclusion is established by the comparison of the date summarised above for before and after treatment of the fuel with Dipetane. Accompanying the specific fuel consumption measurements, at the same intervals, are oxygen concentration measurements showing an approximate 1% absolute (and —33% relative), reduction in excess oxygen concentration in the flue gas. This is consistent with the observed specific power decrease due to addition of Dipetane; both measurements indicate a more complete combustion of the fuel.
This is to an extent consistent with an observed appreciable increase in carbon monoxide concentration after Dipetane addition; I would expect a much larger increase in carbon dioxide concentration. However, carbon dioxide measurements were not attempted.
In summary, the technical measurement data presented by the University of Ulster report shows that the use of Dipetane allows an approximate 10% increase in the efficiency of the boiler in question. This comparison infers that due to the addition of Dipetane to a specified amount of fuel, the fuel is more completely combusted.
Review of "Minch Norton Report on Condition of Boilers Before and After Introduction of Dipetane Fuel Treatment" Summary
Two Cochran Thermax 6500 Kw/hr boilers commissioned in 1990 were examined in 1997 before and after the use of Dipetane as a fuel treatment. Following seven years of use, both boilers had degraded in performance relative to commissioning. The operators note that boiler #1, showing gross efficiency ranges of 78.9-81.8%, is in much better condition compared to boiler #2, as it is nearer to a common fuel heating unit.
The gross efficiency of boiler #2 is not reported. Following treatment with Dipetane the gross efficiency of boiler #1 is reported as 83.6¬88.5%, with boiler #2 at 83.8-87.4%. This is a significant improvement of the order of 10%. In both boilers, a lower fraction of excess oxygen is recorded in the flue gas, corresponding to a more complete combustion of the fuel and consistent with the determined improvement in efficiency.
Review of "Combustion Chamber Deposit Formation Mechanisms" Summary
A very nice, and mostly factual, concise review of the scientific understanding of combustion chambers deposits is provided. Combustion chamber deposits are a composite layered material comprising carbon from the fuel, and partially reduced oxygen from the air. It is well known that combustion chamber deposits form as the result of incomplete combustion due to poor mixing of the fuel/air in the combustion chamber. Though the authors note that at the time of writing (2000), the mode of action is not clearly understood (nor has it been greatly improved since), they show that it is commonly held that combustion deposits inhibit complete combustion through a variety of mechanisms including; radical quenching, and inhibited heat transfer.
Therefore, in addition to the well documented involvement of combustion deposits in limiting engine lifetime, they also retard the ability of the engine to convert the chemical energy of the fuel into useable power. The review finds several pieces of literature that demonstrate that the occurrence of combustion chamber deposits inhibit complete combustion, thus contributing to a cascading degradation in engine performance. The report does not mention Dipetane in any specific way.
However, it is obvious that any fuel treatment that promotes the complete combustion of fuel to carbon dioxide and water, which are gas phase products, will inhibit the formation of engine deposits, which are solids. It stands to obvious reason that this will improve the efficiency and lifetime of the engine.
Review of "Eolas Report" Summary
"Eolas" was an Irish Government Organisation, "The Irish Science and Technology Agency, set¬up circa 1987. It was merged with the IDA in 1993 later being incorporated into Enterprise Ireland. In November 1987, Eolas reported a chemical analysis of Dipetane. The following tests are documented:
- Infra-red and UV spectroscopy.
- Gas chromatography.
- Ash content and ash emission spectroscopy.
- Distillation curve.
- Specific gravity.
- Closed-cup method flash-point.
- Kinematic viscosity.
- Copper corrosion number.
- Elemental analysis.
- Calorific value (energy density).
Each of these tests are routine for determining the chemical characteristics of a material, tests #4, #7 and #9 give important characteristics of liquid fuels, and are each legal requirements for the sale of diesel or gasoline fuel. In the report, the gas chromatograph analysis is omitted, presumably to guard Dipetane intellectual property, as this would give close education as to the actual chemical identity of Dipetane.
To summarise the data, in simple terms, each of the properties measured bare close resemblance to what I know are the properties of a variety of liquid transportation fuel components. There is no evidence that Dipetane bares any properties that are importantly different to the normal constituents of gasoline or diesel. As such, if it is added at small fractions to any normal fuel, I can see no reason to expect any undesirable effects to the engine or wider power train. Similarly, it can be expected that Dipetane would have similar effects to human health and material handling equipment as would diesel or gasoline. Dipetane is shown to have a high flash point and therefore I do not consider it a significant fire hazard. One can expect it to be more inert than diesel and much more inert than gasoline.
Appendix I. Testimonials on the Use of Dipetane
- Novadyne Limited, bus/coach operator, UK, 16 December 2015
- Tanata Valley, bus/coach operator, UK, 11 January 2017
- DRM bus, bus/coach operator, UK, 7 July 2016
- Dawn Meats, truck operator, Ireland, 18 January 2016
- Roadstone Quarry, truck operator, Ireland, 26 June 2007
- Coca-Cola Bottlers Ireland, truck operator, Ireland, 26 August 2005
- McGill Environmental Systems, engine operator, Ireland, 16 January 2016
- Consort Motor Accessories, motor accessories, Ireland, 30 January 2009
- Kelly Fuels, coal and oil distributor operator, Ireland, 6 January 1998
- Car user #1, Ireland, 26 January 2009
- Car user #2, Ireland, 15 August 1998
- Irish Defence Forces, vehicle operator, Ireland, 1 March 2006
- Irish Defence Forces, vehicle operator, Ireland, 24 February 1995
- Irish Defence Forces, vehicle operator, Ireland, 3 October, 1998
- Tru-Blu Oil, vehicle operator, Australia, 11 September 2013
- Blue Express, vehicle operator, Chile, 29 January 2013
- Sealink travel group, vehicle operator, New Zealand, 15 September 2009
- Hooker Pacific, vehicle operator, New Zealand, 20 June 2006
- Peter Keogh & Sons, tractor operator, Ireland, June 2011
- Dr. Stephen Dooley, School of Physics, Trinity College Dublin, Ireland I December 12, 2017
-  R.D. Reitz, Combust. Flame 160 (2013) 1-8 and references therein.
-  Directive 2003/30/EC.
-  Euro 4 (2005) Directive 98/69/EC & 2002/80/EC.
-  Euro 5 (2009) Directive 715/2007/EC.
-  Euro 6 (2014) Directive 459/2012/EC.
-  J. Dec, Proceedings of the Combustion Institute 32 (2009) 2727-2742.
-  C. P. Fenimore, "Formation of Nitric Oxide in Premixed Hydrocarbon Flames", in 13th Symp. (Intl) on Combustion, page 373. The Combustion Institute, 1971.