Part I: Controlled Hydrogen Fuel Assist via Intake Manifold Pre-Mixing as a Combustion Efficiency Enhancer in Multi-Cylinder Diesel Generator Engines: Experimental Investigation on 250–1500 kVA Genset Platforms

This study presents an experimental investigation of Controlled Hydrogen Fuel Assist (CHFA) as a combustion efficiency enhancement technology for multi-cylinder diesel generator (DG) engines spanning 250 to 1500 kVA rated capacities. Hydrogen-rich gas (HHO) was generated on-demand via alkaline water electrolysis and introduced into the engine intake manifold using a pre-mixing strategy at controlled volumetric flow rates ranging from 160 to 750 ml/min, without any modification to engine architecture, fuel injection parameters, or combustion chamber geometry. Experiments were conducted across five representative diesel generator platforms: a V-12 Caterpillar C32 TA engine (1010 kVA, 32.1 L displacement, MEUI fuel system, compression ratio 15.0:1); a Cummins 1500 kVA genset with dual air intake; a Cummins 380 kVA genset with single air intake; a 250 kVA KOEL genset (2012 make); and a KOEL 500 kVA genset (2023 model year, well-tuned CPCB 2 configuration)—operating under CPCB 2 emission norms. Testing was performed under steady-state conditions at 1500 RPM across real-world factory loads ranging from 40% to 80%. The results demonstrate that controlled hydrogen fuel assist yields significant and repeatable improvements in energy output per liter of diesel (kWh/L). For engines with lower injection pressure (CPCB 2 platforms), kWh/L improvements of 8–15% were observed at 40–60% load, while engines with higher injection pressure (CPCB 4 platforms) showed improvements of 4–13% under comparable conditions. A distinct bell-shaped efficiency response was identified, confirming the existence of an optimal hydrogen operating window beyond which efficiency degrades. Comprehensive emission measurements conducted by NABL-accredited laboratories revealed substantial reductions across all regulated pollutants under optimal hydrogen dosing. Particulate matter (PM) reductions of up to 78.2% were recorded on the 250 kVA genset at 80% load with 750 ml/min HHO. On the 1010 kVA Caterpillar DG set, NOx was reduced by 34.6%, CO by 41.4%, and total hydrocarbons (THC) by 48.9% at the highest tested dosing level. The 1500 kVA platform showed PM reduction of 80.1%, NO₂ reduction of 59.2%, and CO₂ reduction of 42.9% at 700 ml/min HHO flow. Notably, exhaust O₂ concentration increased consistently across all platforms, confirming improved combustion completeness and reduced fuel consumption. Critically, testing on the newer 2023-model KOEL 500 kVA genset at Cilicant (Pune) provided direct experimental evidence of the narrow optimal dosing window in well-tuned modern engines: at 12–13 A electrolyzer current, exhaust O₂ decreased and CO₂ increased relative to baseline—confirming over-dosing (Zone C)—while at 7–8 A, CO₂ was reduced by 31.2% and O₂ increased by 22.2%, demonstrating that the beneficial window exists but is substantially narrower than in older engines. This study introduces a three-zone conceptual model (Zone A: negligible influence, Zone B: optimal enhancement, and Zone C: overdosing degradation) to explain the divergent outcomes reported in prior literature. The findings establish that diesel injection pressure, atomization quality, and engine age/tuning state are primary determinants of hydrogen dosing tolerance and that adaptive, load-dependent hydrogen control is essential for consistent efficiency gains across diverse engine architectures. A theoretical combustion framework based on Wiebe heat release analysis and adiabatic flame temperature considerations is presented to substantiate the observed combustion enhancement mechanisms. The paper concludes with recommendations for standardized regulatory evaluation frameworks and long-term durability assessment protocols to support safe and scalable deployment of CHFA technology. Keywords: hydrogen fuel assist, diesel combustion efficiency, HHO electrolysis, intake manifold pre-mixing, kWh/L improvement, emission reduction, CPCB, diesel generator, controlled dosing, transitional decarbonisation Note: Part 1 covers Abstract, Introduction, Conceptual Framework, Methodology, and early Results (Sections 4.1–4.8). Part 2 continues with advanced Results, Discussion, Regulatory/Industrial Implications, Conclusions, and References.