1. Comparison of Clean Diesel and Natural Gas HD Vehicles
Tim Johnson
Corning Incorporated
May 24, 1999

2. Agenda Objectives Approach
To inform ARB of the potential benefits of Clean Diesel technologies as they compare to CNG vehicles.
Approach
1) Show progress in diesel engine and aftertreatment technologies.
2) Look at recent results on CNG vs. diesel
3) Compare emission levels of clean diesel to CNG
4) Relate actual real-life vehicle results from the UK.
5) Compare economics.

3. Emerging Regulations and Health Concerns
Market Drivers for Clean Diesel

4. Tighter regulations are driving diesel to become very clean
4.0/0.05
1/0.05
1.58/0.026
2.0/0.1
3.8/0.04
4.0/0.1
5.56/0.177
g/ bhp-hr
Adjusted for test differences
Tightest tests are assumed (steady state or transient)
Euro IV/V is the Council proposal
HDD: 65% NOx and 50% PM efficiencies will be needed to hit the Euro IV/V standards; 75% NOx will be needed to hit the US2007 assumed standards

5. Diesel engines are coming under much scrutiny regarding toxins
PM2.5, and particularly particles less than 100 nm, deposit in the respiratory tract
Carcinogens and other toxins from Diesel, or general motor vehicle, exhaust are becoming a concern

6. Engine technologies and emissions
Diesel is getting very clean

7. Fuel injection is getting increasingly sophisticated
There is much work on using injection shape control to reduce PM and NOx and improve fuel economy.
30% reductions in NOx and PM and 5% reductions in fuel consumption due to pilot injections and rate shaping.

8. Fine particle number distributions from a common rail HDD engine vary with increasing injection pressure
At high load greater injection pressure keeps distribution the same, but decreases the numbers at low RPM and increase them at high RPM.
At low load, increased injection pressure creates more fine particulates.
EPA SAE
7.9 liter, 144 kW engine
Scanning mobility particle sizes (SMPS) showed minimal effects of dilution ratio from 50:1 to 560:1.

9. Variable Geometry Turbocharging (VGT) and EGR Cut NOx 10-40% under low load conditions in a 1.8 l Euro III engine
Low Load: VGT drops NOx 45% at baseline fuel consumption.
High Load: VGT/EGR could not be optimized, no NOx reductions
Ford SAE

10. EGR drops NOx about 40%, regardless of what else is added
12.7 L Heavy Duty Engine
Detroit Diesel Series 60

11. Cooled EGR or SCR, and Traps will be Needed
Euro IV
Euro 3 HDD engines will have “common rail”, high-pressure fuel injection with rate shaping VGT, and electronic engine controls
60% NOx and PM reductions will be necessary to hit the corner of Euro 4
Cooled EGR with Traps hits corner, but has 3% fuel penalty vs. Euro 3
SCR hits NOx, but may require 40%PM reduction

12. Advancements in Diesel Particulate Traps
2+ orders of magnitude reductions in particulate numbers

13. Retrofitting Off-Road Diesel Equipment with Catalysts & Filters Significantly Reduced Emissions
PM -3 to 50% 80-95%
20% typ.
NOx 0-17% 2-15%
12% typ.
Nescaum SAE
Emissions reductions from DPF and oxidation catalysts depend on the equipment
25% of Big Dig off-road (Boston tunnel) will be equipped with DOCs and passive DPFs.

14. The VERT Study on LDD & Off Road HDD Showed Filters Significantly Reduce PM and Gaseous Emissions
Filters reduced PM by 99%+ by number, but only 70% by mass
EC: elemental C
OC: organic C
Filters reduced PM by more than 99% by number at all load points
Sponsors: Swiss & Austrian Accident Insurance Agencies, German Association of Construction Professionals, Swiss EPA
Considering reform fuel and fuel additives, filters had the greatest impact on reducing PAHs. New lubricants, catalysts, and engine controls are also effective in curtailing PM
Filters reduced CO by 40%, HCs by 85%, and NOx by 25%. No secondary emissions were formed
VERT SAE

15. Diesel particulate filters are very effective in reducing particulates
These two studies and several more have shown that DPFs remove 95+% of ultrafine particulates, bringing emissions down to gasoline levels

16. Continuous Regenerating Trap
One of the new technologies that reduces toxins and particulates is the CRT system
Continuous Regenerating Trap
NO is first oxidized to NO2: NO + 1/2 O2 = NO2
The NO2 then oxidizes the soot: 2NO2 + 2C = 2CO2 + N2
Net: one pollutant eliminates the other
NOx/soot ratios are important

17. JMI CRT System is very effective, but requires low-S fuel and min
JMI CRT System is very effective, but requires low-S fuel and min. NOx/C
AVL SAE
A minimum NOx/PM ratio of 8:1 was determined to be needed for CRT operation. It is generally available over most of the operating range.

18. Advanced diesel aftertreatment systems are very effective in reducing pollutants
The CRT reduces hydrocarbons and CO by >90% under the conditions of the study
The soluble organic fraction (SOF) of the PM was reduced by >70%
The two aldehyde toxins were significantly reduced
NOx was not affected

19. 70+% reductions in NOx and toxins
NOx and HC Treatment
70+% reductions in NOx and toxins

20. SCR drops NOx levels 70 to 75%
12.7 L Heavy Duty Engine
Detroit Diesel Series 60

21. NOx Traps are Evolving for Diesel
91% NOx eff. at 2000 rpm/2 bar
Very low sulfur levels are needed (<10 ppm)
Diesel engines can be run rich enough to desorb NOx traps, with only 2% penalties in smoke & fuel efficiency
FEV SAE

22. Catalysts Performance on Toxic Emissions
mg/bhp-hr
Toxic Hydrocarbon Compounds Reduced by 58% with 368 ppm S Fuel
MECA: API Diesel Issues Forum 4/99

23. Increased catalyst loading will reduce toxins by 80%, but 50ppm sulfur fuel is needed to keep SO4 down
Higher catalyst loadings are effective for reducing all non-PM emissions.
Low - S fuel (50ppm) is needed to control PM emissions, especially at the high Pt loading that is most beneficial for toxin reductions
Pt loadings:
A 0 g/l
B 0.02
C 0.2
D 2.0
Hino SAE

24. Clean diesel technologies are effective for both new and retrofitsPM
Traps will take out 99+% of particles
Traps will take out 70 to 95% of PM mass
soluble organic fraction gives lower percentages
engines can be tuned to minimize SOF
NOx
EGR gets 40% reductions
SCR gets 70%+
NOx Traps are emerging at 70 to 90%
HC and Toxins
60 to 95% reductions with catalysts or traps
depends on sulfur

25. Compressed Natural Gas Emissions
CNG emissions are low

26. CNG vehicles emit 60 to 95% less PM and 0 to 30% less NOx than equivalent diesel vehicles
Buses and airport vehicles
Colorado School of Mines SAE

27. Choice of CNG Engine management technique is critical to controlling emissions
High CNG NOx due to insufficient lean operation at high load. Early mixer type engines
High CNG NOx due to insufficient lean operation or ignition retard.
Depending on CNG engine management strategies, CNG may have higher NOx levels or fuel consumption then diesel.
Closed-loop stoichiometric TWC reduces CNG emissions. Fuel economy suffers
WVU SAE

28. Relative emissions depend on driving behavior
With non-aggressive driving in CBD cycle, CNG NMHC emissions are double, NOx is 50% less, and PM is 97% less than diesel
With aggressive driving in CBD cycle, CNG NMHC emissions are 10X, NOx is 30% less, and PM is 97% less than diesel
WVU, Colorado School of Mines, NREL SAE

29. CNG with catalysts have reduced emissions vs
CNG with catalysts have reduced emissions vs. diesel, but advanced aftertreatment can make them similar

30. In the critical sub-100 nm range, CNG particulate numbers may not be much different from diesel
ELPI used for measurements
Millbrook Proving Ground SAE

31. The U. K. City Diesel Experience
City buses and refuse trucks are going to clean diesel instead of CNG

32. “Diesel buses are becoming very clean indeed” Simon Brown, Principle Engineer, London Transport Buses
Two years ago, only one supplier of “City Diesel”. Now, the UK is going low-sulfur across the country. Price differential is 1.4p/liter.
On old engines, City Diesel and Oxidation catalysts go a long way.
On newer engines, City Diesel and the CRT were very clean.
Euro 2 Engine
Pre-Euro 1 Engine

33. London Diesel buses are cleaner and more fuel efficient than CNG or LPG buses
“it is beginning to look as if the most beneficial and cost effective solution is high quality, fully reformulated Diesel combined with exhaust aftertreatment. We will have 50% of our bus miles on City Diesel by December 1997.” Simon Brown
No deNOx technologies

34. “For refuse collection vehicles, the lowest cost and cleanest alternatives were City Diesel and a CRT” Alison Simmons, Principle Pollution Control Officer, Walsall Metro. Borough Council
Emissions are roughly equivalent to a catalyzed CNG truck
CNG truck lost 7% of payload
Annual operating cost of CRT was -11% vs. CNG and +18% vs. std. Diesel
Capital cost of CNG buses was 7 to 20% higher than CRT (BP127,000 base)

35. Economics - Diesel is $20,000/yr/bus cheaper
No CNG retrofits are feasible
need to replace significant numbers of vehicles to see impact
two fuel services will be needed
Infrastructure costs are high
$40,000 to $60,000 per CNG bus incremental difference; clean diesel may be $2000 to $5000
$500,000 (10 buses, 2-3/hr refueled) to $5,000,000 (200 buses, 30/hr refueled); clean diesel requires low-sulfur fuel - marginal infrastructure
Operating costs are higher
-10% vs. +50% more equivalent energy; +35% typical
+15% more maintenance
$50,000/yr/bus for CNG vs. $30,000/yr/bus for diesel; amortization and overhead
Source NYC MTA private communication

36. Summary
Diesel engine technologies have come a long way, and have significant potential
Diesel after-treatment technologies can make diesels as clean or cleaner than CNG
Clean diesel technologies are much cheaper than CNG and can be retrofit or purchased new
California is well-positioned to take advantage of clean diesel technologies, with emerging supply of low-sulfur fuel