Hydrogen and diesel hybrid engine testing

Since the 1970’s, researchers have been creating hybrid hydrogen and diesel engines. In 2022, engineers from UNSW Sydney successfully retrofitted a diesel engine to run as a hydrogen-diesel hybrid engine at an incredible ratio of 90% hydrogen to 10% diesel by energy fraction.  

Compared to conventional diesel engines, hybrid hydrogen-diesel engines, also referred to as HHO and diesel hybrid engines, offer advantages such as: 

  • Reducing greenhouse gas emissions from hydrocarbons up to 90% 
  • Reducing exhaust gas temperatures from 50-150 F 
  • Reducing organic particulates between 10-70% 
  • No external hydrogen fuel source requirement  
  • Improved durability and engine performance  
  • Vastly lower diesel fuel requirements and costs  

Additionally, compared to 100% hydrogen engines, HHO-diesel hybrid engines are easier to mass produce as any existing diesel engine can be easily modified into a HHO-diesel hybrid engine. Moreover, when combined with batteries or external electric charging, hydrogen diesel hybrids can generate hydrogen onboard using electrolysis, eliminating the need for an external hydrogen fuel source, only requiring a supply of pure water and electricity. 

Improving diesel engine hydrogen injection testing 

Alicat’s mass flow controllers and pressure controllers are used in research studies to increase the efficiency of diesel hydrogen engines and hydrogen injection, such as in a study at the University of Politehnica of Bucharest (UPB). In particular, Alicat’s mass flow controllers can be used to supply a controlled flow of hydrogen into the injection system while Alicat’s pressure transducers can be used to measure pressure within the combustion chamber.   

HHO-Diesel engine system components and operating conditions   

Typical diesel engine hydrogen injection components include separate diesel and hydrogen supply tanks, pumps, mass flow controllers, injectors, pressure transducers, water-heaters (for stabilizing chamber temperature conditions), surge tanks, PLC or computer systems, and gas analyzers.  

Operating conditions for the HHO-diesel hybrid engine design with the 90-10% hydrogen to diesel injection mix include:

  • Chamber temperatures of 90°C maintained by a water heater/cooler system
  • Injection pressures of 10 Mpa for hydrogen and 100 Mpa for diesel
  • Flow rates of 1.44 g/s for hydrogen and 800 cm3/min for diesel

Flow regulation for hydrogen injection  

In HHO-diesel engine test stand experiments, Alicat’s mass flow controllers such as MC-Series or CODA KC-Series are able to precisely control the inlet injection flow rates of hydrogen in order to ensure correct chamber mixing ratios across ranges of engine loads.  

Combined with a PLC or a computer for automation, Alicat’s mass flow controllers adjust in milliseconds to desired setpoints, allowing for accurate flow rate monitoring and adjustments to determine precise measurements of engine operating conditions such as emissions levels, NOX levels, exhaust temperatures, fuel cyclic quantities, combustion rates, etc.    

MC-Series features and specs: 

  • 0.5 SCCM full scale to 5,000 SLPM full scale with a turndown of 0.01% – 100% of full scale 
  • NIST-traceable accuracy up to ±0.5% of reading or ±0.1% of full scale 
  • Repeatability ±0.1% of reading + 0.02% of full scale 
  • Control response times as fast as 30 ms 
  • A range of analog, serial, and industrial protocol communication options  

CODA KC-Series features and specs: 

  • 40 g/h full scale to 100 kg/h full scale with a turndown of 2% – 100% of full scale 
  • NIST-traceable gas accuracy up to ±0.5% of reading or ±0.05% of full scale, whichever is greater 
  • Repeatability ±0.05% of reading + 0.025% of full scale 
  • Control response times as fast as 500 ms 
  • A range of serial, and industrial protocol communication options  

Pressure measurement for HHO-diesel engine testing  

During hydrogen diesel engine testing, Alicat’s high temperature P-Series pressure transducer improves the accuracy of pressure measurements taken within the combustion chamber at different back pressures when simulating cylinder pressure conditions across the compression stroke while at a constant injection pressure.  

Some key features and specs include: 

  • Full scale ranges from a maximum of 0–3000 PSIA and a minimum of 0–15 PSIA 
  • Pressure measurement ranges of 0.01% – 100% of full scale 
  • NIST-traceable standard accuracy up to ±0.25% of full scale 
  • Repeatability of 0.08% of full scale 
  • Measurement response times less than 10 ms 

FastTrack Ordering

M/MC mass flow meters and controllers that ship in just 3-5 business days.
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2 SCCM - 500SLPM


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