1975

Research in 1975 examined hydrogen enhanced gasoline in lean combustion. John Houseman and D.J Cerini of the Jet Propulsion Laboratory produced a report for the Society of Automotive Engineers titled "On-Board Hydrogen Generator for a Partial Hydrogen Injection Internal Combustion Engine", and F.W. Hoehn and M.W. Dowy, also of the Jet Propulsion Lab, prepared a report for the 9th Intersociety Energy Conversion Engineering Conference, titled "Feasibility Demonstration of a Road Vehicle Fueled with Hydrogen Enriched Gasoline.

1977

Conducted research using hydrogen as a supplemental fuel to gasoline on a 1969 production engine. Their research specifically demonstrated that the higher flame speed of hydrogen was responsible for being able to extend the efficient lean operating range of a gasoline engine. They successfully used a methanol steam reformer for in situ production of carbon monoxide and hydrogen.

Lean-mixture-ratio combustion in internal-combustion engines has the potential of producing low emissions and higher thermal efficiency for several reasons. First, excess oxygen in the charge further oxidizes unburned hydrocarbons and carbon monoxide. Second, excess oxygen lowers the peak combustion temperatures, which inhibits the formation of oxides of nitrogen. Third, the lower combustion temperatures in­crease the mixture specific heat ratio by decreasing the net dissociation losses. Fourth, as the specific heat ratio increases, the cycle thermal efficiency also increases, which gives the potential for better fuel economy.

2002

Research done in 2002 shows that the "addition of hydrogen to natural gas increases the burn rate and extends the lean burn-limit". Also concluded was that "hydrogen addition lowers HC emissions", and with properly "retarded ignition timing" also reduces NOx emissions.

 Further research in 2002 achieved results showing "a reduction of NOx and CO2 emissions", by modeling an on-board hydrogen reformer and "varying the efficiency". The research was specifically a "numerical investigation" done to "foresee performances, exhaust emissions, and fuel consumption of a small, multi valve, spark ignition engine fueled by hydrogen enriched gasoline". 

2003

In 2003 Tsolakis at Alabama University of Birmingham showed that "partial replacement of the hydrocarbon fuel by hydrogen combined with EGR resulted in simultaneous reductions of smoke and nitrogen oxides emissions (NOx) without significant changes to engine efficiency".  Similar results have been presented by a team of scientists from Zhejiang University, China, which found that "a little amount of hydrogen supplemented to the gasoline-air mixture can extend the flammability of the mixture... improving the economy and emissions of engines".

2004

Test results in 2004 show "that the H2 rich reformate gas was an excellent NOx reductant, and can out perform raw Diesel fuel as a reductant in a wide range of operating conditions". This is referring to Diesel fuel being used in excess, as a reductant, to cool the combustion reaction, which indeed has a mitigating effect on NOx production.

In 2004 research was conducted concluding that an "SI engine system fueled by gasoline and hydrogen rich reformate gas has been demonstrated" to achieve a "dramatic reduction of pollution emissions". This was achieved by "extending EGR operation" in addition to consuming "gasoline and hydrogen rich reformate". Emissions results show that "HC-emissions as well as NOx-emissions could be reduced to near zero". Overall a 3.5% reduction in CO2 emissions was achieved during the "FTP test cycle" The research also concluded that the exhaust after treatment system can be simplified, "resulting in cost reduction for the catalysts".

2006

Two key challenges facing Natural Gas Engines used for cogeneration purposes are spark plug life and high NOx emissions. Using Hydrogen Assisted Lean Operation (HALO), these two keys issues are simultaneously addressed. HALO operation, as demonstrated in this project, allows stable engine operation to be achieved at ultra-lean (relative air/fuel ratios of 2) conditions, which virtually eliminates NOx production. NOx values of 10 ppm (0.07 g/bhp-hr NO) for 8% (LHV H2/LHV CH4) supplementation at an exhaust O2 level of 10% were demonstrated, which is a 98% NOx emissions reduction compared to the leanest unsupplemented operating condition. Spark ignition energy reduction (which will increase ignition system life) was carried out at an oxygen level of 9 %, leading to a NOx emission level of 28 ppm (0.13 g/bhp-hr NO). The spark ignition energy reduction testing found that spark energy could be reduced 22% (from 151 mJ supplied to the coil) with 13% (LHV H2/LHV CH4) hydrogen supplementation, and even further reduced 27% with 17% hydrogen supplementation, with no reportable effect on NOx emissions for these conditions and with stable engine torque output. Another important result is that the combustion duration was shown to be only a function of hydrogen supplementation, not a function of ignition energy (until the ignitability limit was reached). The next logical step leading from these promising results is to see how much the spark energy reduction translates into increase in spark plug life, which may be accomplished by durability testing.

2008

Using hydrogen as an additive to enhance the conventional diesel engine performance has been investigated by several researchers and the outcomes are very promising. However, the problems associated with the production and storage of pure hydrogen currently limits the application of pure hydrogen in diesel engine operation. On-board hydrogen–oxygen generator, which produces H2/O2 mixture through electrolysis of water, has significant potential to overcome these problems. This paper focuses on evaluating the performance enhancement of a conventional diesel engine through the addition of H2/O2 mixture, generated through water electrolysis. The experimental works were carried out under constant speed with varying load and amount of H2/O2 mixture. Results show that by using 4.84%, 6.06%, and 6.12% total diesel equivalent of H2/O2 mixture the brake thermal efficiency increased from 32.0% to 34.6%, 32.9% to 35.8% and 34.7% to 36.3% at 19 kW, 22 kW and 28 kW, respectively. These resulted in 15.07%, 15.16% and 14.96% fuel savings. The emissions of HC, CO2 and CO decreased, whereas the NOx emission increased.

2010

HHO system addition to the engine without any modification resulted in increasing engine torque output by an average of 19.1%, reducing CO emissions by an average of 13.5%, HC emissions by an average of 5% and SFC by an average of 14%

2015

Petrol engine performance and emission analysis are conducted with Petrol + HHO and petrol respectively. Thus the performance and emission analysis results are compared after conducting the tests with petrol on reduction of fuel consumption in gasoline+HHO and petrol respectively. The following conclusions were observed: 1. the use of HHO in gasoline engines combustion efficiencies, consequently fuel consumption by 20%. 2. Use of HHO in gasoline engines leads to reduction in emission of harmful pollutants such as carbon monoxide and unburnt hydrocarbons. 3. use of HHO in gasoline engine increases the power output of the engine around 5.7%. 4. the HHO gas kit can be easily constructed and easily integrated with existing engines at low cost. 5. thermal Efficiency increases around 5%