From a pollution control standpoint, the 4-Stroke engine technology of the 4-Stroke push mower reduces the emissions of unburned hydrocarbons (HC) to 2.5-4.5 grams per kilowatt-hour from the 67%-82% of the two-stroke model’s 12-15 grams per kilowatt-hour. According to the United States Environmental Protection Agency (EPA) statistics in 2023, nitrogen oxide (NOx) emissions of four-stroke engines are 0.8 grams per liter of fuel and merely a quarter of that for two-stroke engines, and the particulate matter (PM2.5) emission concentration is merely 5μg/m³, meeting EU Stage V emission (from 2025). Performing tests commissioned by the California Air Resources Board (CARB), the 4-stroke push mower on 2 hours of weekly operation has an approximate annual carbon dioxide emission of roughly 22 kilograms, 38% lower than that of the two-stroke equivalent, and equivalent to that of sequestering 1.2 poplar trees.
On fuel efficiency, the fuel combustion efficiency of the fuel blend of the four-stroke technology is 89%-93%, reducing the fuel use of the 4-stroke push mower to 0.35-0.6 liters per hour while conserving 40% of fuel compared to the two-stroke equivalent model of the same power. Take the Toro 22-inch model, for instance. Its fuel expenditure in processing 1,000 square meters of grass is just 2.5 yuan, and the duration it takes to complete the work of the same area is 25% less than that of the electric one. A 2022 University of Bonn (Germany) study shows that commercial lawn mower energy consumption intensity with four-stroke technology across its entire life cycle (10 years) is 0.38, significantly lower than for two-stroke and lithium battery motors at 0.62 and 0.51 (including carbon in manufacturing batteries).
As far as noise pollution parameters are concerned, the sound pressure level when the 4-stroke push mower is in use is 85-89 decibels, 12%-15% less than the 96-102 decibels of the two-stroke type, and in compliance with the ISO 11094 noise regulation (90 decibel limit). In 2021, Japan’s Ministry of the Environment monitored at Tokyo’s center and found that the mean noise transmission distance of four-stroke engines was 30 meters less than for two-stroke engines (89 decibels at 1 meter can be lowered to 50 decibels in just 8 meters), which successfully eliminated 70% of local community noise grievances. The EU eco-label certification requirements indicate that the four-stroke engine reduces the structural vibration intensity (RMS value) by 45% compared to the two-stroke engine, and the axial amplitude is reduced from 0.8mm to 0.45mm.
Sustainable production and scrapping disposal ratio, the proportion of steel components in 4 stroke push mower accounts for 65%-75% (15% is the proportion of aluminum engines), the 40% decrease of plastic usage is realized compared with electric type, and the proportion of scrapping material recover can up to 92%. Honda’s 2023 report stated that its four-stroke engine remanufacturing rate was 78%, and a single refurbished engine could eliminate 56 kilograms of carbon emissions. The whole life cycle environmental cost (producation, use and disposal) of four-stroke models in the EU WEEE directive is 42 euros per unit, 18% lower than lithium battery models. This is primarily due to the modular nature of the fuel system and 15-year lifespan (90% longer than two-stroke models).
Environmental protection balance vs. electric equipment: Although the four-stroke model has direct emissions, in regions where the proportion of coal-fired power in the power grid is > 50% (such as North China), the total-cycle greenhouse gas emissions of the four-stroke push mower (350kg CO2e) are less than those of the electric model (400kg CO2e), based on the 2022 life cycle analysis by Michigan Technological University. Involving battery production and charging emissions. Only when renewable energy’s contribution to power supply accounts for over 75% will electric vehicle models demonstrate environmental advantages and highlight the practicality of four-stroke technology in the era of energy transformation. Based on the all-around evaluation of environmental protection indexes, the 4-stroke push mower is still the ecological optimal solution for most circumstances under current technical conditions.